Disney is in the process of acquiring 20th Century Fox but with the deal unlikely to be finalised until next summer, we're not going to see the X-Men arrive in the Marvel Cinematic Universe in Avengers 4.
That's a shame but possibly for the best, especially as there's already enough happening in that and Avengers: Infinity War without throwing new mutants into the mix. However, Joe and Anthony Russo have clearly been giving the X-Men some thought because they've now revealed which character they would have added to the roster of The Avengers or Guardians to take on Thanos had it been possible.
Joe immediately made it clear that "it would probably be Wolverine" before Anthony added: "Yeah, maybe one day." It's not clear what the future holds in store for the Russos after Avengers 4 is released but assuming they remain in the MCU, we could very well see the filmmakers take charge of an X-Men or Fantastic Four movie in order to ensure that the quality of their adventures greatly improves.
Which X-Men character would you choose to put in Avengers: Infinity War if you had the chance?