Ever since Marvel struck a deal with Sony to bring Spider-Man into the Marvel Cinematic Universe, there have been rumors that something similar could happen with the Marvel properties over at Fox. Now, Avengers: Infinity War director Joe Russo has weighed in. If there are any backroom talks about the X-Men joining the MCU he's not aware of them, although, he doesn't discount the possibility that talks could be going on that's not aware of.
As far as we know, right now there isn't talk regarding the X-Men. I don't know if behind-the-scenes there were conversations or if there are conversations happening but we certainly haven't heard of any.
Rumors of bringing the X-Men, as well as the Fantastic Four, the two Marvel properties who still have their rights owned by Fox, have been rumored on and off for years. There have been rumors that the two sides have even had some preliminary conversations, though nothing that implied that a deal was anywhere close to being signed. Comicbook.com asked Joe Russo about the possibility due to the fact that the new mutant related TV series, Legion, was referred to as being part of the MCU by Marvel at San Diego Comic-Con. If Legion was both related to the X-Men and the MCU, then it could potentially be some sort of bridge to bring the two together. Although, from everything we've heard, it doesn't even appear that Legion will be directly related to the X-Men films anyway.
Still, because of the deal that led to Spider-Man appearing in Captain America: Civil War as well as his own upcoming film, Spider-Man: Homecoming , it's impossible to write off the entire concept of an eventual crossover. The Spider-Man brand was in a bit of turmoil following the disappointing performance of The Amazing Spider-Man 2 and while the latest X-Men entry, X-Men: Apocalypse, failed to set any records, it's predecessor Deadpool did, so it's unlikely that Fox would look too closely at any deal that would require them to share revenue in any way., If Fox is looking at looking at a way to save any of their franchises, The Fantastic Four would be the more likely choice, considering the fact that its last film had real problems, and plans for a sequel appear to have been either canceled, or put on a back burner that's so far back nobody can currently see it.
Still, it's also unclear what Fox is planning for the X-Men at this point anyway. While there are a number of related projects planned, including Deadpool 2, New Mutants and possibly a Gambit movie if Channing Tatum can ever find a director, there's no word on what's next for the main series or any of its characters, save the retiring Wolverine. If you were going to do something new with the characters, now would be just about the best time to do it.