And just as another point:
A x-men spinoff can easily look like something totally new and different to general audience. Even the tittle doesnt need the name "X-Men". The more different it looks from the trilogy or FC, the better, this way general people "wont get tired" of more of the same, because it wont be the same.
AND.... here is my point, try to get a great cast... lets say... just as an example:
Joshep Gordon Lewit
and a few more familiar faces
AND a great/talented director.
And then, someone on here tell me this possible spin-off wont be a success.
What? will someone say Fox cant get a great cast like this for a x-men spinoff? no? ok, there you have it then.
Next Big X-Men Crossover
* 2017- X-Men: Age of Apocalypse
Edit: Forget about 2017:
Official announcement -> X-MEN: APOCALYPSE - MAY 27, 2016!!!!