They already did Dark Phoenix
One major issue with the upcoming film? They’ve already covered this territory.
2006’s X-Men: The Last Stand featured a young Jean Grey. It saw the death of the character as well as the rise of Phoenix, her alternate personality. While this isn’t exactly the same as in the comics, it’s enough alike that they’d have to do things completely different in order to distinguish it. Which brings us to our next point …
Next: That human touch may get lost in space.