I can see Sophie doing a good young Jean Grey. I have no problems with this casting - I mean, just because we know them so well in one specific role doesn't mean they shouldn't get a shot in other roles, and this is a good start for moving away from being typecast for her.

Tye Sheridan I don't know about. Same for Alexandra Shipp. Will reserve judgement as always until I see the film, actors these days often surprise me.