Honestly, they can talk about how many characters the X-Men have all they want but they're still hobbled. There's a reason all these characters are lumped into "X-Men", because most aren't strong enough to have movie franchises. If Fox wants to continue getting diminishing returns for their attempts to put out a poor man's Marvel/DC Cinematic Universe, I will have fun watching them hobble. Off the top of my head, the only things that could work for them are:
Deadpool
Wolverine
X-Force
X-Factor
X-Men
There's literally no reason to give any other characters spin-off films. They'd be really reaching. Throw in Silver Surfer and FF to that too I guess, but Fox just can't utilize them fully since they're not in the MCU. FF can only be maximized in potential by Marvel itself.
The reason why this stuff works for Marvel, and is eventually going to work for DC once they pull their heads out their ass, is because they have multiple strong characters and properties who have all proven their worth by holding their own titles for decades. Superman, Batman, Green Lantern, Flash, Wonder Woman, Aquaman, Guardians of the Universe, Justice League, Iron Man, Hulk, Captain America, Thor, Guardians of the Galaxy, Inhumans, Doctor Strange, Ant-Man, Daredevil, SHIELD, etc etc. All are strong characters and concepts who have years of proven worth. No individual X-Men character measures up to that besides Wolverine and Deadpool. When it comes down to it...X-Men is still just the X-Men.