As you're no doubt aware, big reveals often come from the most obscure places whether that's a trademark listing or toys. Now, Newsarama theorises that a recent addition to ComiXology may shed some light on what the Avengers: Infinity War sequel will be called: Avengers Forever. Marvel has added the 1990s series to that service and there may be evidence pointing to the two being linked.
That tale featured Earth's Mightiest Heroes assembling from across different eras to then travel throughout the timestream to stop a massive threat. With set photos pointing to time travel factoring into Avengers 4, it's easy to see why the site has put 2+2 together here, especially as claims from the Russos that it may all be "B.A.R.F." related are hard to believe when Ant-Man and Tony Stark were quite clearly seen on set interacting (rather than observing) with the Captain America from The Avengers.
Assuming time travel does come into play in the Avengers: Infinity War follow-up, it would make sense for Marvel to use the Avengers Forever title as a way of both homaging whatever links it could have to this series and as a fitting tribute to the team as the current iteration concludes as Phase 3 ends.
So, nothing is confirmed but this is a solid enough theory and it definitely seems as if Earth's Mightiest Heroes will be travelling through time, especially as rumours are swirling about an older Cassie Lang showing up. This title is also much better than Avengers: Infinity Gauntlet and Avengers: Endgame.