No I don't think Mystique....... AND Wolverine.............. wait......... 😘 😘 😘 😘 😘 ..........ok I'm back........ I really don't want to see Mys........wait...... (just to think about it makes me wanna... 😘 )
Besides, it seems that she and Magneto are having something in the movie, remember when she infiltrated that Stryker's base and said "I'm in" and Wolvie said "She's good!" and Magneto said "You have no idea"??? That sounds like an affair to me......but yes you're right...she was all over Wolvie in X2, but why the hell did she do that for?? I don't understand that... 😕 😑 😒
Ok, this may be just my dream, but here's how i think X-3 should go.
The movie should start out with Gambit breaking into the X-Mansion. He wakes up Wolverine by accident and we see the long awaited Gambit vs. Wolverine battle. After a few of the others have been awoken, Gambit is cornered and surrenders, while catching the eye of Rogue. Upon interrogation, Gambit reveals he was looking for a sanctuary in order to hide from a rich, winged mutant from whom he attempted to steal (*ahem* Archangel *ahem*). Gambit then explains that he thinks he lost him, but Xavier allows Gambit to stay there until he is sure. Angel arrives later, angrily storming the mansion looking for Gambit. Singer can take it from there as to how they are inducted into the X-Men.
As for new villains, Apocalypse would be nice but he has too much of a story behind him to make into a less than 3-hour movie. I would recommend the introduction of Juggernaut, as the obvious step-brother feud and alliance with Magneto won't take much to explain, and hopefully the completion of the Brotherhood with Toad's resurrection, Pyro's obvious inclusion, and the hopeful introduction of both the Blob and Avalanche.
I think it would be cool to have apocalypse show up in the third and then when all hope of beating him is lost, the Pheonix comes to the X-Men. Apocalypse and Pheonix would then duke it out and eventually they both destroy each other, and Pheonix is returned to Jean Grey, and Apocalypse supposedly "dies."