I think a Sony-type deal would include X-Men, but that seemed more likely in late 2015 than now (and I think I need to readjust my attitude because I think I'm still sort of living in the past).
In late 2015, there seemed to be a new sense of cooperation between the studios and the setting of Deadpool seemed ambiguous and I was imagining a scenario in which Fox ended the mess they were creating and started fresh with new X-Films that ignored that sloppy past and rebooted in the MCU.
But that doesn't seem to be happening now and Fox seems determined to fumble blindly and continue with their poorly designed and highly confusing reality.
And as for FF specifically, now that we're getting closer to the reversion date every day, there is decreasing reason for Marvel to do any cooperative deal because they can just wait and get those rights back in a few more years.
A deal in 2015 would have allowed them to integrate Doom, Galactus, Silver Surfer etc. into Infinity Wars, but now that it seems very unlikely that will happen in time, there's no reason to not wait a little longer.
If you think for a second that Fox is going to part ways with the X-Men franchise or share a piece of that pie, I have a bridge to sell you. X-Men is really all that Fox has at this point.
4. Trade the FF for X-Men TV rights...
What incentive does Disney have to do so? You guys greatly over-estimate the value of Fantastic Four. You are looking at it from a fan perspective. It needs to be looked at from a business perspective.
Disney has no incentive to help their competitor build the X-Men franchise. If anything, Disney wants to reduce the value of the X-Men franchise to Fox in order to see the rights revert, as X-Men is popular. By helping Fox keep the X-Men franchise afloat, Disney is making reversion all the less likely.
So what is Disney's incentive for doing so? This isn't Spider-Man that we're talking about, a franchise that can make a billion dollars in a single movie. Fantastic Four is a franchise that didn't make in three movies, what Spider-Man has made in one. Hell, forget Spider-Man, Fantatic Four is a franchise that in three movies has made about as much money as obscure properties like Dr. Strange and Antman do in a single movie. This is a franchise that, in three movies, made less money than a property that no one had ever heard of that focuses on a friggin talking raccoon. Why on Earth would Disney help Fox keep X-Men away from them in exchange for THAT?
Now, your response is going to be that with Disney at the helm, Fantastic Four could make Dr. Strange numbers. But that's the point. Disney doesn't need Fantastic Four to make Dr. Strange numbers. Guardians of the Galaxy, Ant-Man and Dr. Strange have proven that Disney can take ANYTHING and make a killing. Disney could take the Rocket Racer and turn it into a viable franchise. It doesn't need to bargain for Fantastic Four to make a 700 + million dollar movie.
In short, this isn't a cash cow like Spider-Man we're talking about here, where it is worth it to share, despite the headaches that come with sharing another studio's IP. The numbers don't justify it and Disney certainly doesn't need Fantastic Four's rights.
In fact, Disney doesn't need anything Fox has. But do you know what Disney wants? The X-Men. Because that opens up a second Avengers-type of franchise for them. X-Men, in the hands of Disney, could pull in Avengers numbers. And all the spin-off movies could pull in Captain America numbers. And Wolverine's solo, in Disney's hands, could pull in Spider-Man/Batman numbers.
Therefore, it makes no business sense for Disney to do something that makes X-Men more profitable for Fox in exchange for a franchise that means nothing to Disney and isn't particularly profitable (if profitable at all). Disney wants X-Men to start failing. That is how Disney gets X-Men back. By it becoming so unprofitable that Fox stops making it and rights reverse or Fox is forced to liquidate the rights by selling them back. It doesn't get X-Men back by giving Fox something that makes it more profitable and successful in exchange for a worthless franchise.