This is how they can do it...
|A little doodle of Ororo Monroe aka Storm in Adidas Yeezy Boost 350|
Similar to how they brought in Spider-Man, I believe that the X-Men should already be somewhat established or imply that they have already been joining together. One way to introduce the idea of the X-Men would be to bring in Ororo Monroe, aka Storm, into the Black Panther franchise. I won't go into gross details, but Storm is one of T-challa's love interests (officially wife in Black Panther Volume 4: #18) in the comics, so why not start introducing the idea of "enhanced" individuals as mutants through Storm. Maybe everyone in the X-Men are on separate missions, and Storm and BP cross paths for the same goal... Maybe the X-Men pique Wakanda's interest and BP takes interest in Storm. Sure there's the build up of T-challa and Danai, but we've also seen Hulk and Black Widow built up to end up no where. Again this was just to express how I would start bringing in the X-Men to the MCU... How do you think they should bring the X-Men or any other Marvel Team that has not yet been mentioned to the MCU? Let me know in the comments section below.