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.