Doctor Strange was supposed to wear Iron Man's armor in nearly including some incredible scenes. One recent example was Doctor Strange and Iron Man switching suits in Avengers: Infinity War.
Fans first caught a glimpse of this possibility during a Benedict Cumberbatch even filmed this version during production on Infinity War, but the scene was cut from the film, keeping fans from seeing the idea realized on the big screen.
Instead of preventing audiences from seeing this scene play out, Marvel Studios could potentially reuse the idea in some form in Doctor Strange in the Multiverse of Madness. The sequel is likely to explore other realities given its title and that could allow Cumberbatch to play another version of Doctor Strange - one that wears Iron Man's armor. Whether Marvel Studios uses the footage already filmed or borrows the concept of Strange wearing Iron Man armor, there are a few different ways that Marvel Studios could make good on the tease.
With some footage already filmed, it's possible Doctor Strange in the Multiverse of Madness could simply repurpose the footage as part of the movie showing what other versions of Doctor Strange are experiencing across the multiverse. In this scenario, Marvel Studios could even have the opportunity to include a surprise Robert Downey Jr. cameo in the film. Since the scene was reportedly filmed, using this pre-existing footage could allow Doctor Strange 2 to provide a look inside the vast possibilities of the multiverse.
Another possible outcome (which may be more likely) is that Marvel Studios could simply reuse the idea of Doctor Strange wearing an Iron Man suit in Doctor Strange 2. This could be done as the MCU's main version of Strange could come into possession of one of Stark's suits. Marvel could also easily use the multiverse to include another version of Strange who is similar to Iron Mage in the comics and has adopted the Iron Man armor. These are just a few options at Marvel's disposal, but the outcome would be the same. Doctor Strange in the Multiverse of Madness would be able to utilize an idea they previously considered and could have limited opportunities to incorporate it in future movies.
