Build inward, not outward a.k.a. Less really is more
You don't have to comb 50 years of back issues to know that there are a lot of characters under the X-titled umbrella. Too many to mention, really. But while the movies and their sequels have taken up much the same mantra as comic serials in terms of piling on people, in film the reverse is the wiser course. Instead of bunkering down with our established band and getting to know them better, I felt like we continued apace and only skimmed over everyone’s most basic characteristics. If it seemed hard to connect to anyone, the subsequent movie would try to correct the damage by introducing even more new faces, or simply wiping the board and starting afresh in a new time period.
What makes for an expanded merchandising foundation also makes for weak storytelling. One of the reasons the X-books were compelling across such a wide range of readership was that, amidst the action, the turmoil of what was happening was acutely focused through the lens of the characters involved. You felt that you knew each character, partially because you’d spent so much time with them, seeing how each of them reacted under pressure, and learning what relationships they had to their powers and teammates. Movies must do this on a compacted time scale, and can do so effectively, but they can be helped along by having a smaller main cast.
To that end…what about exploring the culture a little? We haven't seen much of the implied world outside the Mansion's sphere, except in the very isolated settings of the Wolverine movie, during the protest scenes in Last Stand, and in brief flashes during First Class. What's the modern world like, day-to-day, in this alternative universe? The closest we get to outside interactions are the ones in X2, in the mall, and, later, with the cops at Iceman’s parent’s house, both of which are antagonistic. Instead of feeling compelled to introduce more and more new things, a smart narrative would build on what’s already been established, taking us along for the ride to whatever is encountered next.