Okay. So, while I am still only hopeful about this happening, it is time for the pros and cons to be weighed out on the scales of speculation (I'd say truth, but hell, I don't have the insider connections to make that kind of call).
So, as I see, these are my hints I am following (Blue P marked text is pro, red C marked text con, default color text with ? is could be either way)
1: P: Watchers in GotGv2. Face it, this is something we hoped for, but never dreamed would be really confirmed. As a hint, it is great as we had thought this was part of the FF rights.
2: P: That background straight from Kirby's FF behind Loki in the TR trailer. Again, as many have said, why from FF#64 when Kirby did just as much in Thor and other Eternal/Celestial appearances to use?
3: ?: This back and forth over the Phase model Marvel seems to be abandoning, and the talk from Fox side that they still have plans for the FF. This could be some hardball open but still veiled negotiations between them over the final price for the deal being done, or both giving up on the deal and walking away. Face it, Phase 4 would be tons more fun if that 4 got the circle around it, and no need to keep phases, if we ain't getting them home. 
4: C: Not even a whiff other than rumor of meetings or other hints at a deal being done, but this could be a "?" as well, as Marvel snuck the Spidey deal in at last minute. 
5: ?: Marvel's recent words that there will need to be a new deal after the current one with Sony for Spidey. This one is definitely a question, as they would really want Spidey for earth stories if there are no FF, and his connection with the FF in the comics would leave us howling, not whining and wondering as we are now about the 1st Family, if they let him drift away with the FF back. 
6: ?: Fox's schedule not showing anything beyond a year out. Almost like they are talking to Marvel about the FF, but have not sealed a deal, so they are holding the threat of scheduling, rather than looking bad like Sony (and they did) after the fanboy bombs of FFINO and ASM2. But, also, letting the hope be there. This could just be a thing where they learned their lesson over the long delayed Gambit movie, or just are sitting back, seeing what the market does to the genre with this level of overload coming out. Better to cancel unannounced things behind the scenes than look foolish if Superhero fatigue actually does set in, and have to publicly pull back from a schedule. (Also lets them do more films in development, with better flex in their release date windows, so that is the real reason I score it as a "?".)
7: C: FFINO and the bad taste in audience mouths from it. Let's face it, this is the real reason we may, like the Mandarin, never see it coming. That film got really bad press, reviews, BO, and left many fanboys and GA fans with a bad case of barf-mouth. The longer this plays out, the better for both studios, but worse for us older fans who are beginning to realize we are not Asgardians, Elders of the Universe, or Eternals, just mere mortals with short lifespans. 
8: P: Marvel going to SDCC on a year with a D23. I believe (but have no proof) that the only reason for that is to drop a bombshell on what is beginning to look like a finally finding some traction DCEU. If the GA ever gets behind the DC side, then Marvel might have to do release date showdowns like two drivers playing chicken with their lights out, not knowing in fullness the other guy's intent (or hand, if you want to do a poker analogy instead). Yeah, the full schedule of upcoming Cosmic Arc/Phase 4 might not come until D23, but they will drop a few well placed info-blasts across DC's bow to let them know they have something fans want. 
Now, I might think of other things, and some will call me on these, but this is speculation. I might (hell, probably am) wrong on some, and maybe all points. We won't know until, in the poker analogy, the hole cards are turned over.