First of all, it should be noted that this article contains some Infinity WarSPOILERS, so read ahead at your own risk.
A new rumor suggests that the still untitled Avengers 4 will be partly based on some interesting source material. Ever since Infinity War premiered earlier this week, the rumor has gotten even more intriguing, though the idea has been around since last summer. The main idea has to do with time travel and the future as well as the past, which could be based on some aspects of the Avengers Forever comic.
Back in January, some set photos for Avengers 4 found their way online showcasing a clean-shaven Captain America, Tony Stark, and Bruce Banner, all (except Banner) in their original costumes from the first Avengers movie. It looks like they're reliving the epic Battle of New York, which hints at some time travel trickery and some possible alternate timelines in Avengers 4. This is where the Avengers Forever comic comes into play. As for Infinity War, there are a few minor SPOILERS ahead.
The Avengers Forever storyline takes place a full 5 years after the events of Infinity War and has Tony Stark and the surviving Avengers working as Agents of S.H.I.E.L.D. They end up working closely with Hank Pym, developing some new time travel technology that they will ultimately use to go back in time to get a second shot at Thanos. This means that Avengers 4 will at least begin 5 years after Infinity War. Backing up some of this new rumor are the shots of Robert Downey Jr. on the set of Avengers 4 with much grayer hair in a S.H.I.E.L.D. uniform that were leaked recently. Additionally, there have been shots of Scott Lang with Tony Stark as well, bridging the Hank Pym connection.
Infinity War ends with a whole world of possibilities, and this new rumor seems to be the best one out there at this time. As for anything the Russo Brothers do, it more than likely won't be straightforward and will contain twists. That being said, Marvel Studios and the directors won't be able to keep the secrecy intact for Avengers 4 like they were able to do with Infinity War, so it seems only logical that some of the plot will show up before next May rolls around.
Regardless of what happens, Avengers 4 will have a very interesting story to tell after the end of Infinity War. The case for alternate timelines and time travel were talked about for Infinity War, but they weren't used in ways that any MCU fans thought at all, which is making everything a lot more plausible for Avengers 4. Additionally, there could be some pretty interesting post-credit scenes for Ant-Man and the Wasp as well as Captain Marvel. More clues with reportedly come to light when the official title is revealed. This rumor was first reported over at MCU Cosmic.