To match the epic scope of Avengers: Endgame, the MCU will need to expand its multiverse. Several MCU films, including Loki, Spider-Man: No Way Home, and Doctor Strange in the Multiverse of Madness, have introduced new rules and characters that could culminate in an event as monumental as Avengers: Endgame in the MCU’s fourth phase. However, if the MCU’s multiverse truly contains an infinite number of possibilities, it will have to be much larger than what was shown in Phase 4.
There are countless alternate universes in Marvel comics that feature wildly multiple variations of popular figures, ranging from almost exact replicas of their primary equivalents to anthropomorphic animals and other oddities such as zombies. On Earth-838 and Spider-home Man’s universes, the MCU has delved into alternate universes, but until now, it hasn’t gone as far as Doctor Strange in the Multiverse of Madness does. It’s important to remember that the Marvel Cinematic Universe has only scratched a very small portion of what the multiverse has to offer.
A much bigger event, akin to Avengers: Endgame, is established up towards the end of Doctor Strange in the Multiverse of Madness, much like how the Infinity Saga began with a slow introduction and culminated with a franchise-wide crossover event. A strong start, but by the time the MCU’s multiverse adaptation of Secret Wars (or something else) is released, its scope will have to greatly expand. A truly “multiverse of madness” that connects multiple different universes in an unprecedented film is required for the MCU’s second saga to have a satisfactory conclusion.
Overcrowding is a major concern as the MCU multiverse expands. All of the Disney+ shows are part of Phase 4, which already has a significant increase in annual releases. There’s no reason to spend as much time exploring alternate universes as the MCU’s Earth-616 universe. The possibility of future crossovers like Captain America: Civil War can be kept open by naturally contacting new universes. With the return of characters like Sylvie, Black Bolt, What If…Supreme Strange, the multiversal Spider-Man, and others, a live-action Secret Wars event can match the latter.
Doctor Strange in the Multiverse of Madness already demonstrates how future multiverse instalments can expand upon the Earth-838 universe featured in the film. The Multiverse of Madness hints at a long and complex MCU historical past much different from that of the Infinity Saga, for example, with a quick glance at the victory of Mr Fantastic, Black Bolt, Captain Carter, Captain Marvel, Professor X, and Doctor Strange over Thanos. It’s easy to see how the introduction of new worlds could lead to an entire franchise in the Illuminati universe alone. There is no need to go into every universe the MCU introduces, but it does need a fully-fledged multiverse to wrap up this second MCU storyline with an epic crossover as huge as Avengers: Endgame.