It's made sense for the X-Men movies to be centered on the complex relationship between Professor Xavier and his frenemy, Magneto. Their dynamic, in which they basically opposite sides of the ideological coin, have frequently been the focal point of the comics. The movies have relied on that relationship since the beginning with Patrick Stewart and Ian McKellen, then continued it with James McAvoy and Michael Fassbender. But now they are finally moving on, and it's really about time.
Speaking with Vanity Fair, producer Lauren Shuler Donner says "We cannot, once again, explore the Erik/Charles dynamic. So future stories will find new characters to take center stage, which Donner says is "both liberating and makes me nervous." It's not clear whether that means James McAvoy is leaving the franchise, although they could always have him stick around and not share scenes with Fassbender, who is likely gone anyway.
The next movie is going under the working title X-Men: Supernova, or at least it was. Producer and possible director Simon Kinberg tells Slashfilm that it's no longer the current title, although he declined to say what it is...
"It’s not called Supernova. One of the things we do when we make these X-Men movies, to be totally candid, is — any of these movies, it’s on Star Wars, too — is you come up with fake names to throw people off the scent and when you’re out making the movie, the signs that show you where the locations are say Nova, or whatever the fake title is, and people figure it out, and I don’t even know why we do it anymore."
"But at any rate, it’s not called Supernova. That was the code name for it. There’s yet another code name now. What I can tell you is that we’re in early stages of prep on it, and that it’s something that Hutch and I specifically have been talking about, as the producers of it and me as the writer of it, since post-production on Apocalypse, what the story would be and how would do something bold and radical and expand the universe in the same way that Logan feels bold and radical and certainly Deadpool does as well. And that’s where we are with it."
While he didn't confirm the storyline will be another crack at "The Dark Phoenix Saga", he might as well have...
"Well, I can’t comment on what we’re doing with this next X-Men movie, but I think a way to talk about it potentially, is to talk about X-Men: The Last Stand, and then that being a Dark Phoenix movie that we didn’t get quite right. I think of maybe a few mistakes we made in that movie — and every movie has mistakes — but the main mistake we made in that movie was taking the Dark Phoenix story, which is such a vast and profound saga, and making it the subplot of the movie as opposed to the main plot of the movie. I think if we were to make a Dark Phoenix movie in the future, it would be a Dark Phoenix movie about her struggle, and really should be the A plot and the primary of the movie."
There's no other way to look at this than as a big ol' do-over, and Fox has to hope audiences won't hold that against them. Filming should begin later this year so further details should be coming.