The potential for that boat has sailed and passed in my opinion and even still they can't match Marvel in terms of characters. Their are just to many that Marvel has. Fox is a little better then Sony in terms of numbers but FOX has no idea what to do and how to develop the mutants that is in their universe. They are to Wolverine focused and when First Class became the lowest grossing Xmen film they figured it was because Wolverine wasn't in it. They offered Jackman a multi million dollar deal per pic for something like several more films if i'm not mistaken. I'm not even sure if he accepted or not. I just didn't care enough to follow it.
FOX has made the Xmen as everyone knows way to Wolverine focused. Everything is centered around him while no other characters has really gotten any development. The have developed Charles and Erik more and god help us Mystique for reasons that just baffles me. Mystique is a villain, always was and now they are trying to make her like an anti hero or something because of Jennifer Lawrence'ss popularity. I mean announcing the possibility of a Mystique solo film???? What? I'm sorry but the Xmen has way to many rich characters that deserve film long before Mystique should even be considered.
I'll be fair and say with a good writer and director with vision I believe any character can have a good film even if the box office numbers are so so, even Mystique. Yes she is a complex character but who wants to see a Mystique film, even if it's well done. She is a supporting charter at best and functions as henchman of the main villain. Yes she's had solo efforts in the comics but she just isn't interesting enough to build a movie around. Sorry but FOX don't get it at all.
This is pretty much my perspective, and why I'm not worried about oversaturation of comic book movies on the public at the expense of the MCU if Marvel Studios trades its FF properties for full rights to the X-Men characters and a bunch of X-movies plop out as a result to spite Marvel Studios future Phases.
No matter how many dynamic characters exist in the X-verse, thematically every X-men movie or spin off deals with the same thing. Man vs. Mutant. "They hate us because they fear us." Some variation on that riff in every single story. If Fox was to expand this into 2-3 movies a year, you'd be hitting the same nail over and over and over and over again, whether it's a Gambit film or an X-Force film, almost seasonally through a calendar year. The comic publishing wing can get away with this because the persecuted mutants always represented on a certain level the persecuted comic book collector--one of the reasons the mutants were so popular. But the public at large, if having it shoved down their throat more often, would probably have enough, "Geez, we get it, peace love and rock and roll let's move on." But if you go away from that and just tell a straightforward X-Men vs. the Brood movie that makes no mention of man vs. mutant...the franchise would sacrifice its core value and identity that won its niche fanbase--sizable in the comics realm, unknown in size in the public at large. It's a low ceiling for Fox and the mutants thematically.
Likewise, some of the most popular and distinct storylines from the comics have already or will be adopted by 2016 (Dark Phoenix...Origin...Days of Future Past...Apocalypse...requisite "Magneto as the bad guy" story).
Meanwhile, Marvel Studios can shift thematically from one genre to the next in a shared universe when they release 3 films a year. Mythology, horror, cosmic sci fi, war, geopolitics, techno-thriller...without being constrained by "We Have Something Important To Say That is Socially Relevant Pay Attention Please" drumbeat. Each new film and new genre increases the intrigue of the shared MCU, not detracts from it. Which is what made Marvel comics so great, how interwoven it's universe that included such diverse concepts as Silver Surfer, Shang Chi, Power Pack, and Son of Satan.