Marvel's Illuminati all hailed from the same alternate universe, according to the writer of Doctor Strange in the Multiverse of Madness. Speaking with ComicBook.com, Michael Waldron dismissed fan theories that the group -- which included Charles Xavier, Reed Richards, Maria Rambeau, Baron Mordo, Black Bolt, and Peggy Carter -- came from Earth-838, the canonical home of the Illuminati in the film. Fans have wondered since the movie's release whether some of the Illuminati might be variants from other Earths, and obviously the door is still open for Marvel to decide they were...but as far as the writer is concerned, doing so would be a retcon, not the original intent of the scenes in which the characters appeared.
It remains to be seen whether the actors who played the roles of Reed Richards and Charles Xavier might reprise their roles when and if those characters show up in Earth-199999, the designation given to the Marvel Cinematic Universe's main Earth. While the variants seen in Multiverse of Madness were all played by the same actors as their Earth-199999 counterparts, we have seen variants in Loki that are quite different from their "main" counterparts.
"I think they're all -- for me -- all of those characters are from 838," Waldron said simply when asked what the script's intent was.
There are no official plans for an X-Men movie in the MCU yet, although Deadpool 3 is being actively developed. Waldron also said that Deadpool
You can see the official synopsis for Doctor Strange in the Multiverse of Madness below.
Now that Iron Man and Captain America have left after a fierce battle in Avengers: Endgame, former genius surgeon and the strongest magician of them all, Doctor Strange, is expected to play an active role as a central figure in the Avengers. However, using his magic to manipulate time and space at will with a forbidden spell that is considered the most dangerous has opened the door to a mysterious madness called "the Multiverse."
To restore a world where everything is changing, Strange seeks help from his ally Wong, the Sorcerer Supreme, and the Avengers' most powerful Scarlet Witch, Wanda. But a terrible threat looms over humanity and the entire universe that no longer can be done by their power alone. Even more surprising, the greatest threat in the universe looks exactly like Doctor Strange.
Doctor Strange in the Multiverse of Madness is in theaters now.