Brand New Day - just playing devil's advocate
Alright so we all pretty much expect Sadie to play jean grey but let me drop this idea real quick.
So in almost every scene we see her in, she's covered almost head to toe. What if she's actually playing Rogue. She discovers her powers early on and learns that touching normal people renders them unconscious, maybe she killed someone holding them for too long or touching them for too long which is why she's so covered up. Maybe she finds a telepath who hasn't discovered their powers yet but she touches them and absorbs their powers and is able to manipulate people like Jean does.
Now let's talk about frank and peter. Neither are trying to hurt her, Frank is trying to protect her(maybe she reminds him of his daughter), Peter is just trying to stop her from hurting his neighborhood. Eventually the 2 realize this and work together to try and stop her.
Let's talk banner now, rogues powers will render a human unconscious. What if she touches banner rendering him unconscious and hulk comes forward as he almost always has to protect banner. But this isn't smart hulk anymore because banner is unconscious so it's savage hulk that comes out instead. Maybe he looks grey because of the unconscious banner.
It's probably still jean but I like the idea it could be rogue