i like that idea as well! here's mine:
x4: night of the hellfire
(the reason itll be subltiled is becuase itll involve the main villians to be the hell fire and still have sentinals in it hence the "night of" half title, since the tv show had "night of the sentinals")
this movie would have magneto at a weakened state, the hellfire knowing this they want to use him to recruit phoenix as she has gone missing. This introduces emma (even tho a villian) as a very bad girl. Emma would hold wanda hostage in order to get mags attention, since the hellfire plans to use phoniex and make her stronger, something prof x calls "dark phoniex" where the whole world will be at mercy. the subplot is that the government is rebuilding alcatraz after x3 so the create sentinals to track down strong mutants or rebellios ones (enter gambit and jubilee). with the ending being hellfire vs the xmen (lineup being kitty,jubilee, gambit, wolvie, rogue, colosuss, storm, angel, icman and cyc and beast) but the real winner would be magneto with even stronger power and his agian recruited brotherhood (sabertooth, toad, wanda, calisto,mystique,multiple man, blob, pyro) defeat the hellfireclub while xmen fight of sentinals since magneto now has a huge grudge with the hellfire. rogue gets her strength and flight in this movie and cyclops returns...but returns different, with the memory of a man with ruby blood eyes, which is the ending of this movie intro ducing mr sinister for x5 also jean would fight the phoniex towards the end to finally only become the jean we know. I think the whole who is the badder bad guy is a cool storyline and leaving the xmen in the middle to fight off both guys ya know.