First things first: I think it's ridiculously awesome that Marvel has apparently re-secured the film rights to Fantastic Four, Dr. Doom, Silver Surfer, and Galactus. Fox has demonstrated — on three separate occasions now — that they simply do not know how to present compelling versions of these characters and, for all its tremendous success, the MCU has, I feel, suffered somewhat by their lack of involvement; it just really didn't feel whole to me without them or Spider-Man involved. So assuming it's all true, now they will be, and just in time for Phase Four and The Avengers: Infinity War. Trust me, I couldn't be more pleased about this idea.
But that's it. The circle would then be complete, as far as I'm concerned. I do not want to see the X-Men join the MCU at any point in the foreseeable future, because I have long believed that the X-Men and all other mutant titles should be kept in a separate fictional reality from the rest of the Marvel Universe altogether.
Now please, allow me to explain...
The Marvel Universe as we know it began with Stan Lee's and Jack Kirby's Fantastic Four title in 1961. Over the next year or so, they'd also introduce Ant-Man, Hulk, Spider-Man, Thor, and Iron Man before premiering X-Men. What each of those previous characters had in common was that they all attained their powers or came upon the scene through freak occurrences. Whether it was mad science gone wrong, mad science gone right, or an alien arrival, each of these characters found their new roles through ridiculous happenstance.
The X-Men, on the other hand, instead came about through natural genetic mutation. As foreign as it may have seemed, it was actually just one more link in the chain of mankind's evolution. They were all from here, and they were all born this way. It wasn't bonkers; it was innately wired into the human condition.
This created two differing types of super-powered reality within the Marvel Universe: 1) The world of a ludicrous sequence of events that people were just scrambling around to deal with, and 2) The world of human progression inevitably coming at the expense of human comfort... with people then just scrambling around to deal with that as well.
"What does it matter?" you may now be asking. "Who freaking cares how these characters got their powers? It's all made up, right? So whatever, lemme see Captain America's shield deflect a Cyclops energy blast already, killjoy." And to be clear, this is a perfectly fair and valid point; there's really not a whole lot to argue with.
And yet, that kind of thing has never stopped me from trying.
So here's why this all matters to me: the presence of each in the other's reality ends up, in a way, undermining them both. A world in which crazy stuff happens isn't as crazy or interesting when a significant portion of the population is already heading in that direction, and only growing as the generations go by. A Hulk, Spider-Man, or Captain America will soon be just another Bruce, Peter, and Steve in this world; all it will take is for evolution to simply run its course.
And on the flip side, the entire idea of mutation and the threat of natural human progress begins to unravel somewhat in a world where gamma radiation, radioactive spiders, and super soldier serums can do that work for anybody. The prevalence of these freak occurrences changes the equation of that naturally evolving reality entirely, and makes the very idea of being a mutant both less intriguing and less relevant within its own world.
This is why I want these two realities kept separate: so each can be free to explore its own resulting themes and stakes, without the interference of the other one diminishing/muddling those distinct themes and stakes. I want there to be superheroes made through random chaos, and those made through that which is unavoidable, and I wanna see what each reality can do/find within their respective bubbles.
If Fantastic Four really is on its way to Marvel Studios, then we will get the chance to see how that might play out. We'll have our "Sh!t Happens" universe, and we'll have our "You Can't Stop This Sh!t from Happening" universe. I wanna see that happen, and then watch it develop, at least for a little while.
Then, after it has run its course good and proper, we can have our powerful energy blasts colliding with our Vibranium shields...
Because yes, that would be pretty sweet.