Warning! Spoilers ahead for Doctor Strange in the Multiverse of Madness
While Marvel may decide that they want to cast a new Reed Richards for the MCU's Fantastic Four film, that doesn't mean John Krasinski's time as Mr. Fantastic has to entirely end after his appearance in Doctor Strange in the Multiverse of Madness. The MCU has established the beauty of the multiverse and the concept of variants, but the comics have particularly depicted Mr. Fantastic as a hero who's more than equipped to interact with several versions of himself existing beyond his universe. If Marvel Studios were so inclined, the comics have long provided the perfect way for them to cast a new Reed while still keeping Krasinski's Mr. Fantastic.SCREENRANT VIDEO OF THE DAY
Created by Jonathan Hickman and Dale Eaglesham in 2009, the Mr. Fantastic of Earth-616 discovered the existence of the Council of Reeds, an interdimensional think tank of various versions of the same hero working together to solve all manner of problems. Established by three Reeds who each wielded their universe's Infinity Gauntlet, the Council was based in the space between universes. While the original version has since been destroyed, a new iteration was eventually kickstarted and is still operating in the present Marvel Comics Universe.
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The Council of Reeds could serve as the perfect vehicle for John Krasinki's Mr. Fantastic to stick around, existing as an alternate Reed should Marvel Studios cast someone else for their primary Earth-616 Richards to lead the Fantastic Four. Despite being murdered by the Scarlet Witch along with the rest of Earth-838's Illuminati in Doctor Strange 2, Krasinski's Reed Richards could either be the same variant from an earlier time before his death or could simply be a new version from a different universe.
It should be noted that a failed attempt to form a council of variants has already been seen in the MCU. As was detailed by He Who Remains in Marvel's Loki, he and several of his variants attempted to work together for every universe's betterment just like the Council of Reeds. However, they eventually fell into a multiversal war as certain variants such as Kang sought to conquer rather than aid the multiverse. Interestingly enough, He Who Remains and Kang are both variants of the same man: Nathaniel Richards, a future descendant of the 20th century's Reed Richards. Perhaps it will be revealed that Nathaniel was inspired to study the multiverse by his ancestor and his own council of variants.
The multiversal Council of Reeds is the perfect way for the MCU to have their cake and eat it too if they want to cast a new 616 Reed. Abandoning Krasinki after a single cameo would be very unfortunate and a big missed opportunity seeing as how the actor had long been topping internet fan-casts for years before Doctor Strange in the Multiverse of Madness. Whether Krasinki becomes the MCU's primary Reed Richards or not, the Council of Reeds would be an interesting way to frame Mr. Fantastic as a core multiversal hero regardless. Reed could successfully work in tandem with his variants, dynamically adding to the heroics with his family in the MCU's upcoming Fantastic Four film.