In the past, Marvel Studios has never been one to keep fans in the dark for long on their movie titles; The studio once infamously released its entire Phase 3 lineup on a random Tuesday, leaving fanboys satiated years in advance before the release dates. That's what makes Avengers 4 such an oddity, the final film of Phase 3 but still without a title (and no, it's not Infinity Gauntlet). Originally the film was billed as Infinity War Part II, but that plan evidently changed, and whatever Avengers 4 is now, it's apparently too big to reveal just yet.
Kevin Feige said as much just recently, revealing that announcing the true title of Avengers 4 would be "a big spoiler" for the events of Avengers: Infinity War. Whatever goes down in Infinity War is going to be massive and when it all comes to a head in Avengers 4, it will leave the MCU "very different," per Feige. Could some kind of soft reboot be on the way for a fresh jumping off point following the end of Phase 3? It seems likely. With that assumption and the fact that most Marvel movies are adaptations of comic storylines, we got to thinking of what Marvel stories could possibly be the inspiration for Avengers 4.
Marvel is no stranger to resetting the status quo, having made it the centerpiece of their event comics for the past decade. While none of these stories will likely be word-for-word adaptations (just look at Captain America: Civil War for example), these following stories had huge ramifications on the Marvel Universe and could be serviced to fit quite nicely following Infinity War.
One of the younger storylines on this list, but no less important, Infinity is one of Marvel's better event comics in recent memory. Written by Jonathan Hickman, the sci-fi comic tells a space-faring tale that involved the entirety of the cosmos. The Avengers leave Earth to join the rest of the galaxy in stopping a group of god-like beings from wiping out the universe. While they are away, Thanos takes the opportunity to invade, forcing the Avengers to race back and confront him on their home turf. The story was epic in scope and full of grandeur, as the Earth's heroes stepped up to bat on a universal scale.
True, elements of this story have already found their way into Avengers: Infinity War, such as the introduction of The Black Order, a group of Thanos' elite henchmen. Perhaps following Infinity War, the Avengers are left indisposed and Thanos goes to Earth to get revenge? While the cats are away, the big purple space mice will play, or so the saying goes.
This is one of Marvel's most well-received storylines, one that takes place entirely in the cosmic corner of the comics. It finds Annihilus, the bug-like warlord of another dimension, invading the galaxy with a seemingly unstoppable army, forcing characters like Nova, Ronan the Accuser, Peter Quill, and Super-Skrull to form an alliance to even hope to overcome the odds. One part sci-fi, one part war story, the event saw thousands lose their lives, with our heroes as the underdogs, which only makes their eventual victory all the sweeter. Marvel does not own the rights to Annihilus (Fox does), but they could find a substitute of some kind. The important part is that the galaxy is almost brought to the brink of destruction, and is saved by the hard work and sacrifice of a big cast of characters. None of the Earth characters were in the story, but they can always sub in for others. I can see Thanos (who plays a big part in Annihilation) ripping a hole to an invading dimension with the Infinity Gauntlet, forcing the Avengers and the Guardians of the Galaxy to fight completely foreign enemies.
Note: Annihilation: Conquest, the sequel to Annihilation, featured Ultron as the main villain doing almost the same thing that Annihilus did. It'd be pretty logical to mix the two and have Ultron return in the wake of Infinity War with the whole universe in his sights.
The Thanos Imperative
Assuming that Thanos sticks around following Avengers: Infinity War, this could potentially be the perfect follow-up. The Thanos Imperative was the culmination of years of storytelling and saw the Guardians of the Galaxy and Nova forced to team up with Thanos to defeat an invasion from the Cancerverse, an alternate dimension (Marvel was a real fan of those) where death did not exist. The event ended with Star-Lord and Nova trapping themselves in the Cancerverse with Thanos in a final attempt to keep the universe safe from the Mad Titan. Much like before, let's assume that Thanos abuses the Infinity Gauntlet and it's powers and tears a hole open to the Cancerverse. Now the Avengers and Guardians have to work together with Thanos to save the galaxy. Plus, how cool would it be to see Star-Lord and, say, Iron Man stay behind to seal Thanos in the Cancerverse? It would certainly make the movie more memorable by forcing us to say goodbye to two of the most well-liked characters in the MCU.
Secret Wars (1984)
Secret Wars. The big papa. This is arguably the biggest event Marvel has ever done, which saw the A-List of Marvel's heroes and villains teleported to an alien planet to wage war with each other for an experiment by a near-omnipotent being known as The Beyonder. It was hugely popular in 1984 and later saw a spiritual sequel in 2015's Secret Wars, which is also really good. With so many characters at its disposable, perhaps now is the time for Marvel Studios to adapt this comic, while it still has Robert Downey Jr. and crew under contract. This probably could never be a straight up adaptation, but maybe Earth's Mightiest -- thanks to some recent universe-saving actions -- have gotten the attention of The Beyonder, who strands them on a planet for his own purposes. If Thanos isn't dead by then, he could be along for the ride, possibly filling in Doctor Doom's role and temporarily stealing The Beyonder's power. It would sure as hell be one epic way to end Phase 3.
Important: Spider-Man gets the symbiote (Venom) in Secret Wars, so, there's that to look forward to also.