As we’ve already seen plenty of times with the Marvel Cinematic Universe’s Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness, the merest hint of alternate realities will lead to dozens upon dozens of names being rumored for cameo appearances, and no matter how wild they sound on paper, they can’t be 100% ruled out, either, especially when the driving force of the entire plot means that nothing is outside the realm of possibility.
The Flash is also no stranger to the multiversal casting carousel, with names as disparate as Danny DeVito, Arnold Schwarzenegger and Christian Bale all having been linked to the project. Of course, the Scarlet Speedster has never headlined his own feature film before, so the majority of theoretical returnees have tended to be those from the various Batman projects we’ve seen over the years, and insider Grace Randolph is now claiming that Robert Pattinson could show up in the movie, too, which is currently scheduled to hit theaters eight months after his and Matt Reeves’ reboot.
#DCEU included the multiverse, so that's why I included #TheBatman
I also heard R-Patz could show up in #TheFlash if his movie is popular enough, albeit briefly.
Early days on that stuff though.
— Grace Randolph (@GraceRandolph) March 28, 2021
Everyone involved in The Batman has made it perfectly clear that the film takes place outside of DCEU continuity, and even with the multiverse in play, having fought so hard to extricate it from the confines of the franchise’s connective tissue, you’d imagine Reeves wouldn’t be too sold on the idea of his leading man making a fan-baiting cameo, especially in something that already features Ben Affleck and Michael Keaton as alternate Bruce Waynes.
Then again, Pattinson might be contractually obligated to do these kind of things depending on the terms and conditions of his deal with Warner Bros., but like every other similarly-themed comic book blockbuster in development, we probably won’t know for sure until The Flash arrives on the big screen in November 2022.