Originally Posted by X-Maniac
This film needs to create momentum for future films and be something the franchise can build from.
Shining a spotlight on Mystique when she most likely won't be around any more after DoFP might not be such a good idea. It could make it seem a dead end like The Last Stand if this film wraps up stories for key characters (Magneto, Xavier, Mystique) rather than opens doors for the films to continue.
Thats why they could tease something at the end of the movie, like Jean/Cyke coming back or Apocalypse watching over them.