Spoiler warning: This article contains spoilers for Doctor Strange in the Multiverse of Madness.
Doctor Strange in the Multiverse of Madness introduced the X-Men into the MCU in the form of Professor X. Patrick Stewart's triumphant return as Professor X promises great things to come, but as fans discovered, things ended badly for him. Though the Scarlet Witch killed Earth-838 Professor X, the iconic leader of the mutants still could appear elsewhere in the MCU.
Professor X certainly factors in a future X-Men MCU movie. The multiverse allows other actors to portray the same character, so it remains a question whether Patrick Stewart returns. If he does, it could signal a willingness to incorporate the Fox X-Men franchise into the MCU in the same way it did the Sony Spider-Man movies featuring Tobey Maguire and Andrew Garfield.
X-Men
The X-Men loom on the horizon of the MCU and Professor X's appearance in Doctor Strange in the Multiverse of Madness likely signals the rest of the team isn't that far away. He certainly appears in the eventual movie, though it may not be Patrick Stewart.
Earth-838 Professor X complicates the question of whether the MCU recasts the X-Men. Patrick Stewart retired from the role (and died twice before in the Fox movies) but it seems that love for the actors and the characters may result in other Fox actors returning.
Wolverine
A Wolverine movie also feels inevitable in the MCU. The strong connection between Wolverine and Professor X in the Fox movies probably carries over into the reboot, and the multiverse may help sort out some of the timeline confusion of the previous X-movies.
Hugh Jackman stated his intent to retire from the role, but he seems likely to return at least in a cameo somewhere. Many powerful versions of Wolverine exist in the comics for the MCU to choose from for the next screen iteration, including X-23.
Deadpool 3
Deadpool 3 promises to knock down as many walls between franchises as Doctor Strange in the Multiverse of Madness. Deadpool's connections to Professor X and the X-Men make the third movie a natural place for the character to appear next in the MCU.
Both versions of Professor X from the Fox franchise, including James McAvoy, stand to cameo in the movie. Anything is possible since the Deadpool franchise already takes liberties with established characters like Colossus and Juggernaut.
New Mutants
The multiverse allows the MCU to pick and choose from the Fox X-Men legacy if it wants to. That likely includes The New Mutants. Professor X instructed the comic book team for years, making this a likely spot for his next appearance.
The New Mutants took liberties with the comic book version of the team, but some elements of the 2020 movie make sense in the MCU. Anya Taylor-Joy's performance as Magik does in particular, and her mystical power to cross dimensions makes her a natural character to carry over.
Secret Invasion
Comic book fans know the Illuminati emerge in the Marvel Universe in the aftermath of Secret Invasion. They existed before that, but they came out of the shadows in this major event. Professor X likely joins them in Earth-616 if they appear in the upcoming streaming series.
Events likely play out differently in the MCU given the circumstances, but Professor X makes sense as a cameo in the series, perhaps in flashbacks. The Illuminati formed after the Kree-Skrull War in the comics, an event that hasn't happened in the MCU, at least not that fans are aware of.
Fantastic Four
Professor X potentially makes his next MCU appearance in the upcoming Fantastic Four movie. Earth-838 Reed Richards suggests that the MCU may present a very different version of the team than fans may have initially expected, and the MCU FF may come from the multiverse.
If they do, they may already share a link to Professor X and the X-Men. Reed Richards also potentially serves on the Illuminati council in Earth-616, where Professor X could appear alongside other iconic characters from the comics.
What If..? Season 2
Now that the X-Men reside in the MCU, Professor's next screen appearance comes anywhere within the franchise. That includes What If..? season two. The animated series offers a lot of exciting potential for introducing other X-Men as well.
Doctor Strange in the Multiverse of Madness utilizes the theme music from X-Men: The Animated Series, one of the best animated superheroes shows, which creates a fun opportunity for the MCU to crossover not just in live-action but in animation as well.
Loki Season 2
Loki season two likely explores the consequences of breaking the Sacred Timeline. With so many new timelines and universes created, Professor X stands to exist in at least some of them, making the series a possible candidate for his next MCU appearance.
The second season probably picks up on the concept of incursions established in Doctor Strange in the Multiverse of Madness and may visit Earth-838 or one similar to it as Loki tries to make sense of what Sylvie did at the end of season one.
Illuminati Movie
Professor X and the Illuminati play a key role in several major Marvel Comics events. The best comics featuring the Illuminati detail the secretive council's attempts to manage crises in the Marvel Universe and could be fodder for an MCU movie.
From the Kree-Skrull War to exiling Hulk to Sakaar, the Illuminati make a lot of bold and often shocking decisions. The Earth-838 Illuminati showed a similar tendency in the MCU, and Professor X could be at the center of the Earth-616 version.
Scarlet Witch Movie
The Scarlet Witch brutally murders Earth-838 Professor X in Doctor Strange in the Multiverse of Madness, leaving some fans to wonder if this is the last time they'll see either. Professor X likely returns in a potential Scarlet Witch movie, perhaps to rectify what happened before.
Professor X tried to help Wanda in the movie before she attacked him, and that empathy may open doors for other variants or a Wanda with the power to rewrite reality. Wanda alters reality on a grand scale in the comics, as she did in House of M.