When The Avengers became one of the all-time highest grossing movies, fans immediately began to question whether we'd ever get a superhero crossover featuring Marvel characters whose film rights are owned by another studio. Right now Marvel and Disney are only working with characters they're allowed to use, and that doesn't include Spider-Man (owned by Sony) or the X-Men (owned by Fox). Fans continue to hold out hope, however, that at some point studios will work out deals that allow for characters to cross over into each other's films, and when that day finally comes it's going to be orgasmic for so many people.
Well guess what -- it may be coming sooner than you think. Recent word from Joss Whedon himself suggested he was adding a brother-sister duo to The Avengers sequel, and EW now confirms through sources that the current Avengers 2 script does indeed feature the brother-sister duo of Quicksilver and Scarlet Witch, whose father is none other than chief X-Men villain Magneto.
Marvel's Kevin Feige wouldn't deny or confirm the news, though he did say the "draft could change six months from now." Both Quicksilver and Scarlet Witch are among characters that are open to both Marvel/Disney and Fox to use, though we've been told it's a first-come, first-served sort of deal and so once Disney/Marvel use them, Fox can't. In the comics, the duo have been used as villains in X-Men stories and heroes in The Avengers stories.
Now this doesn't mean Magneto will be showing up along with his posse, but with a lot of time to go before The Avengers 3 it may be possible to begin laying a foundation that has the Avengers battling and/or teaming up with the X-Men in that third Avengers movie, assuming Disney and Fox are able to work out a deal. If not, fans will just have to enjoy the little nods here and there, like when Quicksilver and Scarlet Witch complain about their daddy issues. C'mon, you know Whedon already has a line or two in the script about that.