Kick-Ass 2 director working on X-Force script with an eye towards directing.
That movie (X-Men/Avengers/Spider-Man) would have far too many characters.
Well, hypothetically, they would certainly need to trim the team rosters a bit for budgetary reasons alone, if nothing else. Maybe four on each side. Use only a couple of the (expensive) heavy-hitters, say Wolvie and Storm on the X-side along with a few less expensive characters (actors). For the Avengers side, Iron Man, Cap and maybe some new characters who haven't been seen yet. RDJ may prove too expensive, so you may have to replace IM with another Avenger as well. Jackman's star power could conceivably make up for the potential loss of RDJ.
Add in Spider-Man, and you have nine leads, without even factoring in the villain(s). Avengers had eight leads (including the villain) and three major supporting characters.
Then they would have to deal with the Quicksilver issue...