Here are the plot lines Marvel seemingly just abandoned as the MCU grew over the years. Known for its interconnected storytelling, Kevin Feige and his team have successfully played the long game when it comes to building the MCU. Seemingly unimportant details from previous films ultimately mean something in its contemporaries, effectively establishing a cohesive universe. However, not all planted plot seeds got pay offs, others were simply cast aside, never to be visited again.
The MCU prides itself for preserving a single continuity since it kicked off in 2008 with Robert Downey Jr. and Jon Favreau's Avengers: Endgame, which was chock full of references from previous films. Whether it's direct crossovers or more subtle Easter eggs, this interconnectivity is a key part of the MCU's appeal and success.
While Marvel Studios crafted a satisfying ending to the Infinity Saga, it left some unanswered questions moving to Phase 4. There are also smaller narratives from MCU's 11-year-history that were supposedly leading somewhere but ultimately didn't - either because they're forgotten or Marvel's plans changed.
Iron Man's Demon in a Bottle
The first shot of Tony Stark (Robert Downey Jr.) in Iron Man shows him holding a bottle of bourbon during his visit to present the Jericho in Afghanistan. Fans of the comics immediately assumed that this was the MCU's attempt in bringing the character's Demon in a Bottle print storyline into the big screen. Avengers: Age of Ultron did show him having a glass, both instances called for it. He stalled Loki while charging his suit in the 2012 film and he mingled during the Avengers tower party after they secured the Scepter/Mind Stone from HYDRA, but otherwise the storyline wasn't revisited.
The Leader
Marvel Studios' may have recasted Bruce Banner from Edward Norton to Mark Ruffalo, but the Louis Terrier film is still part of the MCU continuity. This is evidenced by the re-emergence of Thunderbolt Ross (William Hurt) later on after debuting in the said standalone among other things. One particular tease from the 2008 film hinted at Dr. Samuel Stern (Tim Blake Nelson) eventually becoming the Leader. Stern was exposed to the blood of the Hulk after injecting Emily Blonsky (Tim Roth) with it; and the he last fans saw him, his head was already starting to expand - mimicking the Leader's appearance in the comics. 11 years after, fans still don't know what happened to Stern as he continues to be absent in the MCU.
Other Countries Imitating the Iron Man Technology
After announcing to the world he is Iron Man, the government quickly became enamored with the technology Tony Stark created. In Iron Man 2, he fought to keep his creation to himself, refusing pressure to sell it off. In the iconic senate hearing scene, it's revealed that other arms dealers and even countries are trying to replicate the impressive metal suit for their own use. Once presented with footage of test runs all over the globe provided by government intelligence, Stark said that the replicas are mostly 5 to 10 years away from coming close to a functioning suit. He used this to prove a point that there's no immediate threat that demands the government to acquire his creation. It's been more than the time frame Stark gave in the MCU, and yet, there's no word on any other country or weapons manufacturer successfully creating their own Iron Man suit.
Thor's Nine Realms
The Nine Realms are deemed important in Thor's MCU story. Comprised of Thor: Ragnaork.
Lady Sif’s Absence
As Thor's good friend, Lady Sif (Jamie Alexander) was a staple of the God of Thunder's early adventures in the MCU. Aside from appearing on the first two Thor films, she also guest starred in Thor: Love and Thunder confirmed for Phase 4, there's no indication of Sif's re-emergence in the MCU, leaving fans wondering what really happened to her.
Bruce Banner's Tragic Love Affairs
Bruce Banner (Mark Ruffalo) doesn't have the best of luck when it comes to romances. While his fellow Avengers like Iron Man and Captain America (Chris Evans) had great love stories with the same woman throughout their MCU stints, it doesn't seem like Banner is made for relationships. He has not one, but two affairs that didn't go anywhere since the character debuted in The Incredible Hulk. Despite recasting, the origin movie is deemed canon as previously mentioned, hence why Banner's short-lived relationship with Captain America: Civil War, Infinity War and Avengers: Endgame.
Avengers: Age of Ultron also attempted to introduce a new romance for Banner in Natasha Romanoff (Scarlett Johansson). In the Joss Whedon-directed flick, the pair bonded over their common fears stemmed from their respective past traumas. At one point, they even discussed running away to live a normal life together. That obviously didn't happen with Banner going missing for years until he reunited with her in Infinity War. However, as they fought Thanos and subsequently dealt with the aftermath of his snap, Nat and Banner never got the chance to talk about what really went down between them as she met her end in Endgame.
The Sokovia Accords
Introduced in Captain America: Civil War, Secret Avengers. They continued their operation underground until they emerged in Avengers: Infinity War in preparation for Thanos' arrival.
By Avengers: Endgame, the remaining heroes, including those who refused to sign Spider-Man: Far From Home. As the MCU moves forward with Phase 4, The Sokovia Accords will be left in the past without having proper dissolution.
The Existence of Damage Control
While they didn't have a bigger impact in the MCU until Damage Control hasn't factored in any other MCU narrative since (with plans for a TV show scrapped), with no indication that they will re-appear anytime soon.
