ok in my dream x-movie, psylocke would be in it fromt he start as jeans replacement (due to her telepathy) and the gang would discover that mystique is the son of sabretooth and mystique, because mystique would save his life at some point, but risk a lot to do it.
my perfect x-movie would also include apocalypse as the main bad guy and maybe in a hollywood adaptation of 'the twelve' story, however with a few little additions and tweaks here and there to make the story better and fox any problems.
jean would resurface at the end as dark pheonix but at first it would seem that she has come back to end the apocalypse by destroying...apocalypse...but she would then turn on her x-mates, leaving open the x-4 theme for the dark phoenix.
i wouldnt include magneto this time around either, but id like to include the rest of the brotherhood. perhaps it may be that mystique has taken over from him. that way we can include pyro, toad, the blod and avalanche and maybe even sabretooth, but i figure they would only appear slightly as a mini-battle with the new x-men roster at the begining of the film or something.
i would say that the sentinals may be a good idea to include too, but perhaps only in danger room sessions for now. maybe prof x has learnt of their possible coming and is preparing the x-men to fight them if they do eventually come, but the audience believes at first that they are really fighting sentinals and not in the danger room. mayeb that would be good to open the movie with.
that be all i can think of for now folks.