Technically, the Marvel Cinematic Universe has already told multiple X-Men stories. Disney had acquired FOX years before Doctor Strange in the Multiverse of Madness premiered. If Marvel Studios wanted to, it could make the story of the two X-Men trilogies as well as the several spin-offs canon even if they make it so that they'd take place in an alternate reality or universe. This is a problem it will eventually have to take care of with Ryan Reynolds and Deadpool set to make their MCU debut with Deadpool 3.
Having said that, Avengers: Endgame's directors, Joe and Anthony Russo, might have just hinted at what it would take to make them return to the MCU.
The Russo brothers are the most financially successful MCU directors. The two made their MCU debut with 2014's Captain America: The Winter Soldier. They later came back to direct 2016's Captain America: Civil War. More importantly, the duo was tasked with wrapping up the decade-long story of the MCU at the time with 2018's Avengers: Infinity War and 2019's Avengers: Endgame. Their work on the latter two films would cement them as legends in Hollywood as the pair of films combined to gross nearly $5 billion at the global box office.
The two have since gone on to write and produce other projects outside of the MCU, but it appears that they're not above returning.
Here is what the Russo brothers had to say in a recent interview with AP Entertainment:
"We're always open to it. We love those guys. [AGBO's] really been our focus for the moment. I think, you know, you never say never. And if the right story lines up at the right time, we'll all go back to work."
More importantly, the Russo brothers also had a positive reply when asked if they'd like to come back and reintroduce the X-Men into the MCU.
It remains unclear if and when the X-Men will enter the MCU. Judging from what we have heard in recent times, Sir Patrick Stewart's return as Charles Xavier / Professor X for Doctor Strange 2 was more of a fan-service moment than an actual means of furthering the plot. The closest that we'll get to see someone from FOX's X-Men universe enter the MCU soon is with Deadpool 3, which is believed to include a cameo from Hugh Jackman, who played Wolverine in all of FOX's X-Men films.
But, if Kevin Feige does need help bringing the X-Men into the MCU, the Russo brothers are an ideal pick.
In the meantime, audiences can follow the Russo Brother's upcoming projects on Netflix: The Gray Man, Extraction 2, and The Electric State.