Reportedly, an anonymous user posted on 4chan, revealing what they claimed was a major leak of both Avengers: Infinity War and Avengers 4. The bulk of their predictions for Avengers: Infinity War proved to be correct, with details including the return of the Red Skull and Thanos's sacrifice of Gamora in order to acquire the Soul Stone. Given the accuracy of their Infinity War predictions, there's a high chance they're mostly right about Avengers 4 as well.
The original 4chan thread was swiftly deleted but was preserved on Reddit. According to this unknown source, Avengers 4 is indeed a time travel film, with Iron Man deciding to undo Thanos's "snap."
Now the same leak has made some claims about Avengers: Endgame and if their previous accuracy is anything to go by, these predictions could very well come true. But by all means take these rumours and leaks with a pinch of salt. So here are some of the theories regarding Avengers: Endgame:
According to the leak, only two of the original Avengers survive the movie, with Captain America giving his life in battle against Thanos. Due to changes in the timeline, Mjolnir has been restored, and Cap actually wields the enchanted hammer against the Mad Titan before being killed. At one point, Hawkeye must protect the unfinished Stark Gauntlet, and plays an "instrumental" role in Thanos's defeat. The Hulk and Banner identities, meanwhile, merge into the "Professor Hulk" persona - and Hulk is the one who ultimately wields the Gauntlet against Thanos, losing an arm in the process.
This particular leak is highly believable, and not only because the source's Avengers: Infinity War predictions were so accurate. The first key point is that this potential leak didn't contain a character arc for a hero who disappeared as a result of the "snap." Looking at the actual details from the leak, Infinity War most definitely set up the "Professor Hulk" arc. What's more, Sebastian Stan has teased one particular scene "where everybody was there." This could easily be the scene where Thor and Captain Marvel lead their army of heroes against the Mad Titan.
And since Marvel has said that Chris Evans is not done with Captain America. It makes us feel that he is as Marvel is famous for its misdirections. So if Marvel says ahead of the movie that Captain America won't die. Chances are that he might. Either way, we may have to get our tissues ready.