I think it would be cool if the plot was this...
Phoenix comes back and whatever. She's weak so she stays near the lake pretty much, trying to get strength and get rid of that sickening feeling. As she does this, eventually in the movie she goes nuts and is powered up by the evil phoenix powers, and can just fly the hell home. Meanwhile, the other X-Men are setting up a recruitment for people that haven't taken a side yet, evil or good. One of the main people in this assignment is Beast. They stumble upon Gambit, who is a bit of a rogue. Speaking of Rogue, her powers have to increase, just as the others. Anyway, Gambit and Wolverine have a lot of arguments, and when they have to battle Jean, Gambit wants to kill her while the others don't. Wolverine expresses true leadership skills by working with Cyclops in the fact that they both are responsible for the woman they love. Blah blah blah, Pyro and them should do something but I'm too tired to think. In the end, Beast helps Jean out and she turns back to normal, and then we end off with something like a deal being cut, where we introduce the sentinels or if you wanna go another route, introduce Apocalypse/Juggernaut or another threat. That way, if theres no other ones, we know the story continues, and if there is, boom, we have a plot.