Read everything below. Let it sink in. And then read it again.

Isn't Jessica Chastain playing an interglatic villain?
Also, Magneto is leading a new group of mutants. Again.
Like BigReg said I don't think anyone is that emotional attached to the new Jean or Cyclops for them to pull this off.

http://www.comingsoon.net/movies/news/883783-simon-kinberg-teases-a-grounded-tone-for-x-men-dark-phoenix#/slide/1

Simon Kinberg teases a grounded tone for X-Men: Dark Phoenix

Production is already underway for the upcoming X-Men: Dark Phoenix film, and in the latest issue of Total Film, director Simon Kinberg teased his plans for the film using some unexpected buzzwords.

Speaking with the outlet, Kinberg said that for the film (which he is writing, producing, and directing) to work, he needed to “find a way to ground it so it’s not too intergalactic.” Kinberg added that he considers the X-Men movies to be “human…and emotional,” though it remains to be seen how those qualities would preclude the film (set to introduce aliens to the X-Men films) from being “too intergalactic.”