IMO, they shouldn't bring back Magneto, Mystique and Professor X if they do a X-Men 4 movie. Why? Because I feel like every X-Men movie has to revolve around the relationship of Professor X and Magneto and it doesn't have to.
Magneto was the main antagonist in the original trilogy and he already appeared in First Class and soon he will appear in DOFP. I want the X-Men to face a new villain without Magneto having a role in the movie.
Professor X was the leader figure of the X-Men in the original trilogy, we already know his origin story, he already died. Even if he comes back alive in DOFP, I want to see the X-Men continue without Professor X behind their back, that would be a 1st in a X-Men team movie.
Then for Mystique, I feel like she's one of people's most favorite villains in the series. But I seriously think she needs to graduate in the series. Besides Magneto, she's the only villain who will appear in more than 5 films and I think 5 films is enough for her. There are a lot of female villains in the comic books that haven't been introduced in the movies yet.
So I basically want half of the cast of X4 to be new. I'm keeping Wolverine, Storm and the other X-Men just so it would still feel like X-Men movie (not a new series) and to keep the fans and people who were already familiar with the previous X-Men movies especially the original trilogy.
