With 10 years of continuity behind it, the Marvel Cinematic Universe had an ambitious goal for the capstone Avengers: Endgame. To best play to the strengths of the history the previous films established, the plot of Endgame heavily revolved around time travel. But in playing around with all the cool tricks inherent to this narrative mechanism, Marvel ended up breaking the timeline they worked so hard to create.
After finding out that Thanos, the overarching villain of the MCU's Infinity Saga, destroyed the Infinity Stones that made his culling possible, the Avengers soon realized that their only option was to use Pym Particles to go back to previous points in time when the stones still existed and retrieve them. The stones could undo the damage they caused, but procuring them proved to be a challenge.
The Avengers planned an elaborate Time Heist to pull off their plan, but even after the movie threw shade at other time travel movies (like Back to the Future) for playing fast and loose with their time travel rules, Endgame still did not do very well to cross its t's and dot its i's. There are several nagging details that have been bothering fans ever since Endgame, and even Spider-Man: Far From Home, revealed the present state of the MCU.
Right off the bat, there are complications with the MCU's present timeline. Endgame made a time jump to 2023, so in the interim the movies that come out are technically set in the real world's future. This seems to put Marvel in an interesting conundrum just from a business standpoint: How is the product placement that fuels the financial juggernaut of the world's biggest blockbusters possible when the latest brands they're supposed to feature would be out of place in 2023?
All the car models, billboards and topical pop culture references that abound in MCU movies would already be out of date by 2023. A dozen different aspects of a film key viewers in to its place in history. Perhaps these subtler details are supposed to be glossed over in the ensuing years, but some things no amount of gloss will cover up.
Perhaps most burning: Are there multiple Captain Americas running around at some point in the MCU? Endgame tasked Steve Rogers with returning the stones after the Avengers used them to save the lost half of the universe, granting him ample Pym Particles to make the trips he would need to tie up the film's loose plot threads. But after Cap did his duty he did not return, and instead traveled back to spend time with the love of his life, Peggy Carter.
This left fans wondering if there are multiple Caps, if they replaced one another at any point and how Cap could possibly sit idly by while some of history's greatest tragedies unfolded. Then, of course, there's the problem of the shield. He bequeaths the one-of-a-kind weapon to Sam Wilson after returning as an old man and officially announcing his retirement, but Thanos chopped the shield apart in the film's climax. To remove it from any point in the past would have robbed a past Captain America of his trusty weapon, so where did the new one come from?
Endgame also left a plot thread dangling that is clearly meant to be picked up on later, but in the meantime creates a vacuum of confusion. While going back in time to the Battle of New York the first Avengers film revolved around, shenanigans ensue that allow Loki to escape capture with the Space Stone (then known as the Tesseract). The Avengers are left needing to retrieve the Space Stone from a different point in time, and Loki's fate is left a fat question mark.
A question mark that the planned Loki series on Disney's streaming service, Disney+, will doubtlessly address. A purported log line for the series states that he "uses the power of the Tesseract to travel throughout human history and change historical events." It seems likely Loki's series would take place entirely in this alternate timeline, but the prospects for the state of the MCU timeline seem all the more disastrous in light of what he could do. There are enough problems with the timeline as it is, how could Marvel address these issues in any sensible way?
For the time being, the plan appears to be to push the issue off until Marvel figures things out. The upcoming Black Widow solo film is said to take place before Endgame, meaning that these would be largely moot points for the film's plot. While it is not clear how far back the film will go, the setting may be revealed this weekend at D23 Expo, where first look footage is expected to debut.
It's doubtful that the Eternals film would directly tie in with much of the goings-on of the current cast of characters, given that their iteration in the comics are often depicted as dealing with their own issues. They are also likely to be a risky move given the very low brand recognition there, so, just as Guardians of the Galaxy set itself light years away from the events of its predecessor, Marvel might do well to keep the Eternals at arm's length.
Similarly, the upcoming Shang Chi feature will not necessarily tie in to previously established story arcs. The character is more of a street-level hero in the comics and tends to deal with his own problems, but most importantly it would be quite the task juggling the introduction of a new cast of characters while dealing with an old set of problems.
Which is exactly why Doctor Strange in the Multiverse of Madness will be the perfect opportunity to deal with the problems of the MCU's timeline in a central way. The title itself practically promises to deal with the issue of alternate timelines, but the plot would be a natural fit for the character. Not only is Doctor Strange an already established character featured in four Marvel films, but we know from Endgame that it is part of his duty as the Sorcerer Supreme to preserve the timeline.
It was his predecessor the Ancient One who explained the mechanics of protecting the timeline in Endgame, and without the Time Stone, it could well fall on Doctor Strange to steer the MCU back on course. Whether or not this will put him in conflict with Loki remains to be seen, but this could prove an exciting opportunity to tell a vast array of new stories while neatly finishing old ones.