Would the Elves have considered giving Narya to a human?
The short answer is "no".
There are any number of reasons why the Elves would refuse to give one of the Three Rings to a mortal. The Elves think of us as rather unreliable, immature, selfish, power hungry, and prone to making catastrophically bad decisions, and frankly, they are probably right. Consider our track record:
We began to worship Morgoth almost as soon as we entered the world. Some Elves, just after they were awoken, were misled by Morgoth, but very few of them worshipped him. Later, we proved to be equally willing to obey Sauron.
A good number of the Elves knew better than to trust Sauron from the beginning. The few who gave him the benefit of the doubt did so with serious reservations, and they refused to let him take part in the forging of the Three Rings. As soon as Sauron put the One Ring on, the Elves with the Three realized it, and hid the Three until such time as Sauron was defeated and the Three were safe to use. Humans, on the other hand, accepted the Seven Rings without hesitation, and were immediately turned into Nazgûl.
We were stupid enough to let Sauron talk us into invading Valinor - where the gods live - in an attempt to conquer the Valar and Maiar, and take immortality by force.
When Sauron was defeated in the War of the Last Alliance Between Elves and Men, Isildur took the One Ring to Mount Doom, and with Cirdan and Elrond standing there shouting "GET RID OF IT, STUPID!", he decided that destroying the most evil being in the world was less important than having a pretty new Ring. This meant that the world was doomed to repeat the process at a later date. The fact that the Elves ever spoke to us again is testament to their patience and forgiveness.
On the idea that mortals might benefit from being exempt from the weariness of time:
Humans are already exempt from the weariness of time. We don't live long enough for this to become an issue.
I think the problem here is a simple misunderstanding resulting from the different perspectives Elves and Men held on life and death. Elves are immortal; Men are mortal. Ironically, each viewed the other with envy, and it wasn't uncommon for each to view their own longevity as a punishment, or at least a burden. Since we, the audience, are human, it is only natural that we understand the human viewpoint rather than the Elvish one. We, like the Men of Middle-earth, are destined to live for a brief moment of time, and then blink out of existence; because we are fully aware of this, we might be tempted to dream of the alternative, and paint a rosy picture of immortality. However, as we all know, the grass is always greener on the other side of the fence; therefore, it would be advisable to consider the issue from another perspective.
Both in-universe and out-of-universe, Tolkien refers to human mortality in two ways: "the Doom [occasionally "curse"] of Men" and "the gift [from Eru Ilúvatar] of Men". The former sounds worse than it is; Tolkien is fond of using words in their archaic senses, and the archaic meaning of "doom" is "fate, judgment", which may or may not include a negative connotation. The latter term is unquestionably positive in tone. Mortality is a gift, something we should be thankful for. And it is telling that of the two terms, Tolkien uses the latter far more often. In fact, when the phrase "the Doom of Men" is used, it is almost always by a human character, not by Tolkien himself as narrator.
Here are some examples of the way Tolkien describes mortality in his world:
It is one with this gift of freedom that the children of Men dwell only a short space in the world alive, and are not bound to it, and depart soon whither the Elves know not. Whereas the Elves remain until the end of days, and their love of the Earth and all the world is more single and more poignant therefore, and as the years lengthen ever more sorrowful. For the Elves die not till the world dies, unless they are slain or waste in grief (and to both these seeming deaths they are subject); neither does age subdue their strength, unless one grow weary of ten thousand centuries; and dying they are gathered to the halls of Mandos in Valinor, whence they may in time return.
But the sons of Men die indeed, and leave the world; wherefore they are called the Guests, or the Strangers. Death is their fate, the gift of Ilúvatar*, which as Time wears *even the Powers [i.e., the Valar] shall envy. But Melkor has cast his shadow upon it, and confounded it with darkness, and brought forth evil out of good, and fear out of hope. Yet of old the Valar declared to the Elves in Valinor that Men shall join in the Second Music of the Ainur; whereas Ilúvatar has not revealed what he purposes for the Elves after the World’s end, and Melkor has not discovered it.
- The Silmarillion, Quenta Silmarillion, Ch 1: Of The Beginning of Days
The doom of the Elves is to be immortal, to love the beauty of the world, to bring it to full flower with their gifts of delicacy and perfection, to last while it lasts, never leaving it even when 'slain', but returning – and yet, when the Followers come, to teach them, and make way for them, to 'fade' as the Followers grow and absorb the life from which both proceed*. The Doom (or the Gift) of Men is mortality, freedom from the circles of the world1. Since the point of view of the whole cycle is the Elvish, mortality is not explained mythically: it is a mystery of God of which no more is known than that 'what God has purposed for Men is hidden': a grief and an envy to the immortal Elves...
The 'Elves' are 'immortal', at least as far as this world goes: and hence are concerned rather with the griefs and burdens of deathlessness in time and change, than with death...
Only the 'immortals', the lingering Elves, may still if they will, wearying of the circle of the world, take ship and find the 'straight way', and come to the ancient or True West, and be at peace.
- The Letters of J.R.R. Tolkien, #131
1 Note that Tolkien here refers to human mortality as being both a gift and a doom, whereas he refers to Elven immortality exclusively as a doom.
But the view of the myth is that Death — the mere shortness of human life-span – is not a punishment for the Fall, but a biologically (and therefore also spiritually, since body and spirit are integrated) inherent part of Man's nature. The attempt to escape it is... silly because Death in that sense is the Gift of God (envied by the Elves), release from the weariness of Time.
- The Letters of J.R.R. Tolkien, #156
The Elves represent, as it were, the artistic, aesthetic, and purely scientific aspects of the Humane nature raised to a higher level than is actually seen in Men. That is: they have a devoted love of the physical world, and a desire to observe and understand it for its own sake and as 'other' – sc. as a reality derived from God in the same degree as themselves – not as a material for use or as a power-platform. They also possess a 'subcreational' or artistic faculty of great excellence. They are therefore 'immortal'. Not 'eternally', but to endure with and within the created world, while its story lasts. When 'killed', by the injury or destruction of their incarnate form, they do not escape from time, but remain in the world, either discarnate, or being re-born.
This becomes a great burden as the ages lengthen, especially in a world in which there is malice and destruction. Mere change as such is not represented as 'evil': it is the unfolding of the story and to refuse this is of course against the design of God. But the Elvish weakness is in these terms naturally to regret the past, and to become unwilling to face change: as if a man were to hate a very long book still going on, and wished to settle down in a favourite chapter. Hence they fell in a measure to Sauron's deceits: they desired some 'power' over things as they are, to make their particular will to preservation effective: to arrest change, and keep things always fresh and fair.
The 'Three Rings' were 'unsullied', because this object was in a limited way good, it included the healing of the real damages of malice, as well as the mere arrest of change; and the Elves did not desire to dominate other wills, nor to usurp all the world to their particular pleasure. But with the downfall of 'Power' their little efforts at preserving the past fell to bits. There was nothing more in Middle-earth for them, but weariness. So Elrond and Galadriel depart. Gandalf is a special case. He was not the maker or original holder of the Ring – but it was surrendered to him by Círdan, to assist him in his task. Gandalf was returning, his labour and errand finished, to his home, the land of the Valar.
- The Letters of J.R.R. Tolkien, #181
The real theme for me is about something much more permanent and difficult: Death and Immortality: the mystery of the love of the world in the hearts of a race [i.e., Men] 'doomed' to leave and seemingly lose it; the anguish in the hearts of a race [i.e., Elves] 'doomed' not to leave it, until its whole evil-aroused story is complete.
- The Letters of J.R.R. Tolkien, #186
In this mythical 'prehistory' [i.e., The Silmarillion] immortality, strictly longevity co-extensive with the life of Arda, was part of the given nature of the Elves; beyond the End nothing was revealed. Mortality, that is a short life-span having no relation to the life of Arda, is spoken of as the given nature of Men: the Elves called it the Gift of Ilúvatar (God). But it must be remembered that mythically these tales are Elf-centred, not anthropocentric, and Men only appear in them...
This is therefore an 'Elvish' view... It should be regarded as an Elvish perception of what death — not being tied to the 'circles of the world' – should now become for Men... a divine 'gift'... since its object is ultimate blessing... a 'mortal' Man has probably (an Elf would say) a higher if unrevealed destiny than a longeval one. To attempt by device or 'magic' to recover longevity is thus a supreme folly and wickedness of 'mortals'. Longevity or counterfeit 'immortality' (true immortality is beyond Ea) is the chief bait of Sauron – it leads the small to a Gollum, and the great to a Ringwraith.
- The Letters of J.R.R. Tolkien, #212
As for the Elves. Even in these legends we see the Elves mainly through the eyes of Men. It is in any case clear that neither side was fully informed about the ultimate destiny of the other. The Elves were sufficiently longeval to be called by Man 'immortal'. But they were not unageing or unwearying. Their own tradition was that they were confined to the limits of this world (in space and time), even if they died, and would continue in some form to exist in it until 'the end of the world'. But what 'the end of the world' portended for it or for themselves they did not know (though they no doubt had theories). Neither had they of course any special information concerning what 'death' portended for Men. They believed that it meant 'liberation from the circles of the world', and was in that respect to them enviable. And they would point out to Men who envied them that a dread of ultimate loss, though it may be indefinitely remote, is not necessarily the easier to bear if it is in the end ineluctably certain: a burden may become heavier the longer it is borne.
- The Letters of J.R.R. Tolkien, #245
To highlight the different viewpoints of Elves and Men, we have this passage from The Tale of Aragorn and Arwen; Arwen admits that she had previously believed that men were "wicked fools" for their failure to appreciate mortality; now, as her husband is dying, she finally realizes how agonizing it can be.
'"Nay, dear lord," she said, "that choice is long over. There is now no ship that would bear me hence, and I must indeed abide the Doom of Men, whether I will or I nill: the loss and the silence. But I say to you, King of the Númenóreans, not till now have I understood the tale of your people and their fall. As wicked fools I scorned them, but I pity them at last. For if this is indeed, as the Eldar say, the gift of the One to Men, it is bitter to receive."
'"So it seems," he said. "But let us not be overthrown at the final test, who of old renounced the Shadow and the Ring. In sorrow we must go, but not in despair. Behold! we are not bound for ever to the circles of the world, and beyond them is more than memory, Farewell!"
- The Lord of the Rings, Appendix A, The Tale of Aragorn and Arwen
So why do Elves think mortality is a gift? Consider the issue from their perspective.
Elves are inherently devoted to the natural world and the animals and plants that inhabit it. They love living things, and in many cases, they grow to love humans as well. Their purpose in life is to nurture life, preserve the natural world, and foster growth. They are compelled to heal the wounds of the world around them.
Time passes, and the Elves don't grow old; yet they are made to watch as the things they love age, wither, and die. The trees, the birds, the deer in the forest, the men they come to care for; they all die, while the Elves continue living. This is bearable for some time, and the millennia wear on.
The world is constantly changing, but it is in the Elves' nature to prevent change, to preserve things as they are. This is obviously a losing battle, even with the Three Rings. A small corner of Middle-earth might be kept as it is, as Galadriel managed in Loríen, and Elrond in Imladris, but the larger world cannot be held in stasis; change, decay, death - nothing can stop the circles of the world.
After some time - perhaps 4,000 years, perhaps 10,000, perhaps 100,000 years - the burden of all the death and decay, the endless repetition of the cycle of life, becomes too much to bear. The Elves, being immortal, know that for them, there is no escape from the circles of the world. They can't expect to be released from the wearying ordeal, so the only option left to them is to depart Middle-earth entirely and seek respite in Valinor. Only there, in the Undying Lands, can they find solace from the heartbreaking procession of life and death. Only there does everything remain as it is, forever.
To Elves, immortality is a burden at best, and at times, it must feel like an outright curse. Everything they love, outside of each other, grows old, becomes frail and weak, and ultimately dies. The accumulated sense of loss and heartache must be torturous, especially for beings who are more attuned than any others to the hurts and of the world. They feel the pain of the living things around them, and they take on the sorrow of the suffering they have witnessed.
From this perspective, it is perhaps easier to understand why Elves envy us for our mortality. Their own experience leads them to focus on the blessing of being released from the circles of the world. They see it as a liberation. They have no experience of the fear of imminent death, or the bittersweet emotions of loving someone and knowing that you will soon be parted from them by death. They, like us, are inclined believe that "the grass is greener on the other side".
We don't experience the pain of being forced to watch the world around us decaying and dying, being renewed, maturing, and dying again, age after age. From our perspective, it is clearly preferable to live forever, or at least, to live longer, and have some control over the time at which we leave the world.
