Other than the words "sources at MoviePilot report", I can think of no flimsier source than a producer on a Kevin Smith podcast, but let's hit on this one just in case. Matt Key, a producer on Kevin Smith's Fatman on Batman show, was on Collider Heroes and suggested a deal could be developing between 20th Century Fox and Marvel that would potentially see the X-Men or Fantastic Four crossing over into the MCU.
"I've heard from a few of my sources, my little birds that Fox and Marvel have... kind of talked, but not really, but like there's interest from Fox, like, 'Ooh, y'know, what they did with Sony and Spider-Man is actually pretty cool, like, maybe...' We're years away from that ever possibly happening... but I think that's what it would take... Fox joining hands with Marvel..."
Yeah, "years away". "Kind of talked, but not really". Anything could be years away. I predict there will be a Fox/Sony crossover, but y'know, it's still some years away. Anyway, it's also unlikely Fox suits are in meetings talking about all the cool shit Marvel has done for Sony. They've got enough to deal with getting their own movies ready.
All that said, Fantastic Four is a shambles right now and Fox clearly needs help correcting the course. Could they reach out to Marvel for help some day? Absolutely. It's not likely to be now and we aren't likely to learn about it in this way.