There are times when fan theories go a little far out of the lines, but considering that we’re talking about the MCU and Marvel movies, outside the lines might be about the only way that a story can be taken in order to make sense. But the theory is pretty simple, Charles Xavier didn’t kill anyone, they were pulled into the MCU somehow, and when he was pulled in the degenerative brain disease became that much worse. It’s kind of a simplistic theory that doesn’t appear to go over a lot of talking points that might be brought up by anyone that might want to know more, but right now we don’t really know how the X-Men and other mutants are going to be introduced into the MCU so we really don’t have anything to go on. The bombshell that was dropped during the previous episode of WandaVision when Quicksilver showed up at their home is something that has plenty of people talking at this point and is making it hard to figure out if we’re just being given a giant tease or something that might actually signal the arrival of mutants in the MCU. It’s fair to assume that there have already been mutants in the MCU and that they’ve had to hide away since persecution has been a major thing in the lives of several mutants in the history of Marvel comics, even when they’ve been more than a little heroic.
But what might be kind of fun is if the MCU made use of the fact that there are mutants that can teleport to different dimensions, which, with a little creative tweaking could lead to mutants finding their way to the MCU for one reason or another. Now that The New Mutants has stepped onto the scene it would be great to see Magik use those teleporting powers of hers in such a manner. But there are other teleporters that could possibly make this happen, even if a few of them are a little more obscure than those that have become fan favorites. There are also other ways to make a passage between worlds, and the hope is that the emergence of the multiverse into the MCU will make this happen since people are ready to see the X-Men, but the theory that people are just sucked into one dimension or another is pretty thin. It’s a theory of course and one that a lot of people might be thinking about at this point as far as being one that might make sense, but given the fact that there are other ways of traversing the various dimensions, it’s easier to think that mutants have been in the MCU already, but have been in hiding for a while simply because they’ve been persecuted a time or two and might be leery of showing themselves too often.
If anyone remembers from the comics, Captain America and Wolverine did meet in the past, but Wolverine was going by his given name of James Howlett at that time and it’s fair to say that Captain America wasn’t too impressed with him since he thought that James was a bit of a hotshot. He did mention in the Ultimates that James managed to get up and keep moving through some of the worst times that he could remember during the war, which made everyone think that he was just lucky. It would be way too easy to explain how mutants have already been in the MCU for a while since they would have no real reason to step forward for fear that people would begin to persecute them much as they’ve done for a good part of their time in the comics. But the theories are going to keep coming until the MCU finally includes some of the favored heroes that have been around for so long, as well as the villains since the X-Men have given rise to a different type of hero and villain that are different no matter that they seek the same things as many other characters that have already been established in the movies. By admitting that they’ve been there and aren’t coming from an alternate dimension it might make a lot of people wonder what they’ve been doing since the X-Men are supposed to be so deeply heroic, but again, that persecution, which has never really kept them down before, could have been so bad that they might have simply given up and tended to their own kind for so long until it became necessary to finally stand up.
However the MCU is going to bring mutants in it does feel as though it’s going to have something to do with the multiverse since at this point simply having them in the MCU would likely get a lot of people asking why they never made themselves known. I’ve already gone over it, if people can’t pick up on the idea then oh well.