The events of Avengers: Endgame provided such a satisfactory conclusion to the first three phases of the Marvel Cinematic Universe that there’s been a brief lull in fan speculation about the future of the franchise. However, with Endgame now sitting pretty as the highest grossing movie of all time, Marvel Studios isn’t going to stop making movies any time soon - and the future of the MCU beckons once again.
Phase Three officially came to a close with Spider-Man: Far From Home, and the saga of the Infinity Stones is definitively over. Many believed that Far From Home would serve to set up the MCU for Phase Four and beyond, and while many tantalizing hints were dropped, Marvel's cinematic future is still largely a mystery.
Update: Confirmed! In Spider-Man: Far From Home, Peter Parker is given a pair of high-tech Tony Stark shades that are programmed with an artificial intelligence (E.D.I.T.H.) that can remotely access Stark Industries' databases and an army of drones.
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Some fan theories regarding the future of the Marvel Cinematic Universe are general and overarching, but others are highly specific - and one by Redditor /u/papa_prevail definitely falls into the latter category.
They posit that a scene from Spider-Man: Far From Home in which Peter Parker dons an old pair of Tony Stark’s sunglasses actually holds significant meaning, because Stark’s sunglasses likely contain some high-tech secrets. Specifically, they think Stark’s sunnies will allow Peter to see through Mysterio’s deceptions - and perhaps learn that the giant monsters that Mysterio is fighting are not quite what they seem.
In the trailer for Spider-Man: Far From Home, Mysterio claims that he hails from an alternate Earth in the Multiverse. While the veracity of his statement is highly dubious, it wouldn’t be much of a surprise at all if the Multiverse was coming to the MCU. However, it might not come as a result of Thanos’s snap, but as a consequence of the actions of the Avengers.
According to a fan theory by Redditor /u/jarred_98, the time-travelling shenanigans of the Avengers in Endgame are the actual reason that the Multiverse has come into existence. By creating a series of alternate timelines in their quest for the Infinity Stones, the Avengers inadvertently created a bunch of Earths where things are slightly differently than they are in mainstream continuity - and these new worlds could be explored in future films.
Update: Debunked, but played with. The repercussions of the Snap - which is known as "the blip" in the MCU - are dealt with at length in Far From Home, and Parker and his friends discuss how weird it is that younger students are now older than them and former peers are now in college. However, Harry Osborn and Miles Morales make no appearances.
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As far as we can tell from the Far From Home trailer, Peter Parker and the majority of his friends disappeared when Thanos snapped half the universe out of existence - and they’ve been absent from Earth for five years. However, not all of Peter’s classmates would have been been snapped, so there are bound to be students that were once younger than him that are now in his grade - and that could include some of his classic comic book friends.
A theory by Redditor /u/Bman1738 posits that Harry Osborn - the son of the Green Goblin and Peter’s best friend in the comics - will be introduced as a new classmate of Peter and the gang. Alternatively, Redditor /u/pacificwisdom theorizes that Miles Morales will make his MCU debut in a similar fashion.
A contemporary storyline in Marvel Comics features T’Challa’s nation of Wakanda entering into a conflict with the subterranean empire of Atlantis, led by Namor the Sub-Mariner, one of Marvel’s oldest characters. Fans have been waiting for Namor to show up since the Marvel Cinematic Universe began, and Redditor /u/jajalool thinks the seeds have already been planted in Avengers: Endgame.
When making a report to Natasha Romanoff, Okoye makes reference to underwater earthquakes, which might seem like a throwaway line. Alternatively, however, it could be foreshadowing Namor’s impending arrival - and setting him up for conflict with Okoye and the other Wakandans, perhaps in a Black Panther sequel. Redditor /u/jajalool says, "Namor will be the next villain for Black Panther. The mention of the earthquake under the ocean was a hint towards it. Namor will be mad his people were lost, and will believe that he is superior to the heroes we have."