In honor of the release of Logan, widely acknowledged most likely to be the last time Patrick Stewart will play Professor X:
It strikes me as rather lucky that a bald English actor of the skill and gravitas of Patrick Stewart existed at the right time to play Charles Xavier, and one known in SF circles, to boot. Most people would probably agree to the assessment of this as one of the most perfect and obvious castings in history.
Stewart, of course rose to prominence with the release of Star Trek: The Next Generation in (1987-1994) and he first played Xavier in X-Men (2000) That is a fairly long interval during which the rather obvious cast choice could have been discussed.
What was the first coverage of the suggestion or evidence of discussions that Patrick Stewart should/would play Charles Xavier?
Since the idea was probably alive in fandom for a while before becoming a reality, a complete answer should cover weak sources (e.g. fan art, forums, blog posts) and (later) more reputable sources (e.g. Hollywood news coverage)