In the Voyager episode "The Gift," we see Kes become so powerfully psychic that she leaves the corporeal realm of existence. Memory Alpha states this about her departure from our galaxy in general and Voyager in particular:
Kes began to undergo a massive surge in her mental powers. [...] Kes became telekinetic and was able to carry out delicate surgical procedures using only her mind. Unfortunately, she rapidly started to destabilize at the subatomic level and was causing massive damage to Voyager as a result. Taking a shuttle, she left the ship to explore her new condition and, as she left the corporeal world behind, pushed Voyager out of Borg space, 9,500 light years closer to Earth, as a parting gift. (emph. mine)
Something that she said during the episode caught my attention:
KES: I don't know, and that's what makes it all so exciting. It's as if I can see into a place where the distinction between matter and energy and thought no longer exists. (emphasis mine)
To me, that sounds an awful lot like this:
WESLEY: Is Mister Kosinski like he sounds? A joke?
TRAVELLER: No, that's too cruel. He has sensed some small part of it
WESLEY: That space and time and thought aren't the separate things they appear to be? I just thought the formula you were using said something like that.
TRAVELLER: Boy, don't ever say that again. And especially not at your age in a world that's not ready for such, such dangerous nonsense.
Especially Kes' mention of thought as part of the equation, as well as the ability to hurl ships thousands of lightyears and the somewhat relaxed relationship with Newtonian physics got me wondering:
Did Kes become a Traveler? Did she do so completely under her own power? A Traveler is defined as a being similar to The Traveler; a life-form with incredible super-physical powers, first encountered in ST:TNG's "Where No One Has Gone Before". In later TNG episodes he shows us his extraordinary abilities are attainable by (exceptional) humans, and eventally Wesley becomes a Traveler too (ST:TNG "Journey's End").