When the box-office numbers for Homecoming start coming in, Fox will have to realize they can make more money if they let Marvel make FF and integrate it into the MCU (and Fox shareholders will be screaming for it) The question then will be "Is Marvel interested in a similar deal, or will they just wait for the rights to revert?"
This latest rumor may have been all about Fox trying to convince Marvel they need to deal.
I think the main thing is that Marvel can easily sit back and wait for the rights to revert. They have enough projects on the table to last them through 2027.
Let's be honest. Right now the F4 are damaged goods, and it kills me to say that. Comic book fans know what a F4 movie in the right hands could be, but I think the majority of movie goers are just going to think "why are they remaking that again?"
Fox needs the deal, Marvel doesn't. With Sony it was different. There was more pressure for Marvel to cut a deal. Spider-man is Marvel's flagship character. To not have him in the MCU just seemed wrong.
The Fantastic 4 are huge within Marvel and you could argue Doom is even more important than the FF. But I don't think there's a huge need to have them in the MCU right now. Not that it wouldn't be awesome.
It's just that I think the dynamics of the situation right now, are that Marvel already got back Daredevil and Electra from Fox without doing anything. Fox is worried about that, but their shareholders would not want the company fronting money for another produced FF movie. I agree with you that those shareholders know Marvel's track record and if they could cut a deal that was mutually beneficial, that's the best bet.
Remember back when all of those rumors were going around that Fox wanted to create a "FCU" with the Fantastic Four interacting with the X-men. Well clearly they don't have the rights to do that, because the simplest thing would just to have the FF in Dark Phoenix. Despite the protests to the contrary by the Fox fanboys, there's zero evidence that Fox can do that.
Fox will either have to come to Marvel with a deal they can't refuse, or the rights will revert. They certainly can have another crack at producing another film, but again outside Deadpool, Fox cannot create a CBM that can crack 250M domestic. The people who do the accounting know this, so it would be silly to act in a way that would further damage the property.