Now it might be possible that Patrick Stewart could be appearing in the upcoming X-Men: Supernova movie that films this year.
In an interesting Instgram post, James McAvoy is featured having dinner with both Patrick Stewart and producer/writer Simon Kinberg in which he posts:
Dinner last night with the man who's in a multi generational three way relationship with two professors.thanks for dinner @simondavidkinberg and @hutch.parker ,I can't wait for the summer.
So from that post, it's possible we could gather that Patrick Stewart might be back, and we also see that James McAvoy confirms his involvement in X-Men: Supernova.
Gathered together by Professor Charles Xavier to protect a world that fears and hates them, the X-Men had fought many battles, been on adventures that spanned galaxies, grappled enemies of limitless might, but none of this could prepare them for the most shocking struggle they would ever face. One of their own members, Jean Grey, has gained power beyond all comprehension, and that power has corrupted her absolutely! Now they must decide if the life of the woman they cherish is worth the existence of the entire universe!