This comes from a thread on the CBR message boards that I frequent during my sober hours. It's a rumor about the upcoming Death of X event that Marvel announced last week. Right now, the prevailing theory is that this event will finally explain just what the hell happened to Cyclops and the entire mutant race after the 8-month time skip after Secret Wars. Anyone who has been following my reviews on this site know that this is a big fucking problem for the recent X-books, especially Extraordinary X-men. When an entire story happens off-panel and fucks over a character that got fucked over enough in multiple X-men movies, it's a big problem. But I digress.
This rumor isn't necessarily about Death of X itself. It's more about what it will lead to in 2017. And while not as batshit crazy as lizard people, it is in the same zip code. It has huge implications for the future of the X-men, both in comics and with Marvel as a whole. And if it turns out to be true in any capacity, I'm pretty sure it means Fox and Disney lawyers are in a full-blown rap war.
Fall is a prelude to a much larger event coming next year called End of X.
Death of X is about a group of mysterious assassins targeting specific X-Men for death, some big names die and the culprits turn out to be a group of people who were being controlled by an unknown intelligence from the future.
End of X comes out next summer. Carol Danvers teams up with Timegazer (he's the new inhuman who can peer into the future from Civil War II; also Carol "wins" Civil War II and the whole thing is much lower stakes and less edgy than Civil War I) to discover a new threat looming, some kind of horrible "storm" that threatens to collapse the timeline.
The "storm" can only be resolved by removing all the mutants from the universe, which sparks big time chaos about how to resolve the issue.
I don't know the exact plot details (doubt anyone does because this stuff isn't usually ultra-thought out beforehand except for the broad strokes plot), but it ends with all the mutants being shifted over to another timeline of their own free will. The 616 goes on without them, and there will still be X-Men books but they'll all take place within their own separate continuity to ensure maximum MCU synergy within the "main" universe.
They've been looking to do this for a while. Folding the ultimate and 616 universes together was to make room for a potential "X universe" down the line, to avoid too many alternate universes running in parallel. Some specific mutants *might* stick around in the 616, but I don't know which.
This rumor doesn't just come from a message board either. Some of the details are the result of a YouTube video that was cited. Since I know searching YouTube is just inviting someone to get side-tracked by cat videos, here's the video I found. I imagine someone at Disney will send multiple take-down notices and flood emails with remixed Frozen songs so watch it while you can.
So what does this mean? Well more than anything else, it means Marvel is just that determined to fuck the X-men over and get them the fuck out of the mainline comics. Marvel is making a metric fuckton of money by focusing on properties they control the movie rights to. Just ask Namor how important those rights are. The X-men, on the other hand, will NEVER get back under Disney/Marvel's wing. After Deadpool generated half a billion in profits for Fox, they will NEVER fucking let them go. I think Marvel/Disney pulling a stunt like this would be their way of fucking Fox over long-term.
That said, I don't think it's very likely. Marvel just went through the trouble of streamlining their comics again after Secret Wars. They just got rid of the festering rectal wart that was Ultimate Marvel. They just started up X-men 92 and have a successful side-world in Spider-Gwen. I don't think they're going to try to fuck up what they went to such lengths to unfuck with Secret Wars. But I've been wrong about this before. Nuff said!