In regards to the "X-Men TV rights rights for the FF movie rights" trade, I believe I read somewhere that since Marvel's TV and Film divisions are separate, you can't simply trade for one to have the other. Fox's TV side worked out a deal with Marvel's TV side to do X-Men TV shows. Marvel is sure to get a cut of the money from it in exchange. Trust me, if Marvel Studios somehow got the rights back to the FF, we would have heard about it. Feige would have made a point to bring it up in the press run for Civil War.
Not saying Marvel has the rights, but if they did, that strategy would be the last they would follow. Think about it. Marvel got the rights late last year after allowing Fox to develop a couple of shows or whatever, it was already too late to integrate any of its members into CW without looking like an obvious shoe-in. They come out and say they have it anyways, GA goes and watches CW which has amazing new characters, character development of old characters, and a great story. Fans will still start wondering, man how would it look if FF was there? Can you imagine a Hulk vs Thing? What about Spidey vs Johnny Storm? Oh man, etc etc.
As others mentioned, if they have it, one of the best places to announce would be at comic con.
I don't think a Sony deal would work for the FF. Spidey moves over $1billion in merchandise annually, so Marvel was motivated to keep Peter as the world's most popular superhero. And even with his recent BO struggles, Spidey is still a cinematic A lister. His presence in Marvel films helps the BO.
As I have mentioned before, unless Marvel is playing the long game and getting the full rights back to spidey, they have given more than I would expect from any Sony subsidiary, ever. That's without counting the rumors and my personal conjectures on it. Anyways, you're right, FF would not get Marvel to give up close to what they did for SM, and at this point (or rather post Fan4stic), they would not give up a lot for them IMHO.
To answer your question, no I don't think Marvel is going to Fox asking to work a deal for the Fantastic Four. Even if they did, Fox would turn them down I believe. Fox and Marvel, or even more importantly Fox and Disney, do not have a good relationship. Rumors are abound that the two companies flat out hate each other. One of the things that always comes to my mind is how Fox is probably pissed that Disney got Star Wars and they didn't. I just don't believe these two companies would ever get along. The only way I see Marvel getting FF back is if the rights revert. That's going to take Fox from completely giving up and I don't think the egos at Fox are willing to do that. They have 4 years to come up with a new plan on the FF and I bet they will figure out a way. They probably know that Marvel would make it work and are not wanting their biggest competitor to get a chance at it. I hope I'm wrong but Fox is too pigheaded to let the rights revert.
Fox execs have mentioned at one point how they wish they could have made a play (for star wars) and how disappointed they were that Lucas didn't at least let them know so they could get in the game. They do have the consolation that they will have SW IV: ANH in perpetuity unless a deal is worked with Disney. I would laugh hard if Disney pulled the chair from under them again and purchased TWX. Hah.
Fox is probably not doing a sequel. They lost tens of millions of dollars on the last one AFTER home video sales, they just had their Torch cast in an MCU film, they're trying to mend fences with Marvel (TV co-production stuff, Deadpool's actually getting a bit of film tie-in merch), and it simply makes more sense to reboot. Now a reboot without Marvel would be a disaster, but the Russos DID say it would be cool to be able to use the Fantastic Four once, and they're the guys that thought it woyld be really neat the get Spider-Man into their Captain America movie...
Someone on this forum, I think, mentioned that there is only one or two merchs that are based off the movie (which Fox would get a percentage of the revenue). Supposedly, everything else is based off the comics, which Fox wouldn't see a dime. I don't remember which merch was based on the movie, or how he knew it was just that one or two, but when I look around deadpool merchandise, I haven't seen any that I said, "that's definitely based off the movie" like I have with CW and BvS.