A cameo by Days Of Future Past's Peter Maximoff (Evan Peters) on WandaVision has lit the flame under a boiling pot of speculation. Theories from fans across the board range from the most predictable to some of the outrageous. Though, the aspect that audiences are overlooking is the implications of Peters' MCU appearance.
Since the Pietro on Wanda's doorstep hails from a different cinematic universe, there's a good reason to believe more of his comrades from the X-Men movies could join him. Even without watching the remaining episodes of WandaVision, the cameos by past Marvel characters in Spider-Man 3 and Doctor Strange And The Multiverse Of Madness are establishing that those different cinematic universes will collide with the prime MCU.
What that means for WandaVision is the Scarlet Witch's father could be next. Peter (Evans) is a modified version of Age of Ultron counterpart. In turn, it's feasible to conclude that Magneto (Michael Fassbender) is joining the show. Easter Eggs like Wanda (Elizabeth Olsen) using a similar fighting stance during her confrontation with S.W.O.R.D. did seem like a hint foreshadowing his arrival. Otherwise, why would Wanda's combat style mirror that of her father's so closely?
House of M
The other clue pointing towards Erik Lensherr's debut is that WandaVision seems to be borrowing quite a few elements from the House Of M comics, which share quite a few similarities with the events we've seen on the show. Between Wanda altering reality to suit her liking and her imagined family with Vision, the two are very alike.
With that known, if the Disney+ series continues adapting portions of House of M, audiences could see Magneto enter the fold. Not only that, but the comics also feature another prominent X-Man who's a viable candidate to add to the show, Professor Xavier (James McAvoy).
Both of these prominent X-Men are pivotal figures in the comics, and with more of House of M involved, the Professor's arrival seems inevitable. The idea of them coming to Wanda's rescue does feel like it would blow open the door for the X-Men exactly how way fans pictured it.
How WandaVision And The X-Men Fit Together
The notion of Professor X, Magneto, and a handful of their comrades arriving in the knick of time to stop S.W.O.R.D. from executing Wanda Maximoff would establish their presence in the prime universe. And in doing so, their stance on superhuman relations will also become public information. The X-Men are known for tackling mutant superhuman threats, while at the same time, they also protect their brethren from prejudiced humans who seek to do them harm. That fact is important because the X-Men defending Wanda would tie-in closely to the public reputations they've crafted over the years.
Another takeaway from this hybrid version of Pietro is Wanda might try to fix him. She recognizes him as her brother, but seeing her other half in a new body could lead to Scarlet Witch reshaping him back to his original form. But in doing so, Wanda may inadvertently set off a shockwave that mutates others in the nearby area. An event of that magnitude could explain the mutant's sudden arrival in the MCU.
While a definitive answer to the question remains unknown, odds are the Scarlet Witch will have a role to play in their introduction. Whether it's intentional or not, the growth of her powers and the limitless extent they appear to have, suggests she's the catalyst that'll put everything in motion.
Nevertheless, WandaVision's latest tie-in with the X-Men Cinematic Universe is bound to lead to more crossovers in the future. It may be one or two like Magneto and Charles Xavier, but there's a possibility that the entire crew from X-Men: Dark Phoenix will join them, too.