

I think you guys are making this way, WAY more complicated than it needs to be. If I'm Kevin Feige, and I'm introducing the X-Men for the first time in an established universe, then this is what I'd do:
First, I'd look at the original comics. The Fantastic Four came first, followed by the Avengers (individually and together), then Spider-Man, and last, the X-Men; which was 2 years later. Mutants didn't exist up until the first X-Men issue and before that, there were many, many other comics. Thus, in the MCU, Mutants will not exist until the first X-Men movie; no matter the films that came before. It's very simple and no arguments necessary. The Mutant gene itself will be explained in the film; again, no arguments necessary. Any problems with the Inhumans existing is negligible as they were regulated to TV, don't have any connections to the MCU, and have been cancelled. People are already forgetting about it....
The first X-Men comic focused on 5 teenage students of Prof. X's school fighting Magneto; it was simple. The 5: Cyclops, Marvel Girl, Beast, Iceman, and Angel all have huge potential to become very popular with children and adults; alike. They can become HUGE toy sellers. Cyclops and Iceman, in particular, have very cool powers and would be a massive hit with kids. Race and sexual orientations are up for debate, but don't get your hopes up.
I'd start with those 5, and expand from there. You don't need to move so quick here. The X-Men have a humongous roster, so why waste them all in one go? You need the first film to be a hit, so start off small. There is potential for 15 or more years of interconnected films, so it's best to save many of the members for sequels. Many of you want this to be the cartoon brought to life. That will be cool, but we should wait for it. Marvel wants the audience to always be craving more; we know we'll get it eventually.
Any talks of the Fox films needs to die because there is no way in Hell that Marvel is keeping this universe. It makes no sense in terms of MCU narrative, and even less so from a box office perspective as the FoXmen are a sinking ship. Apocalypse sucked, and it's cast sucked too. They're not strong enough to headline a MCU movie, so out they go. Throw in the stink of the Bryan Singer lawsuit, and it's over. The end. Kaput.
