I would have to surmise they finally drop the phrase missing since the beginning and make the title: Avengers Assemble.
They have refused to have Cap say that phrase and since all those people ended up breaking down into little parts, they would have to be reassembled. Also, with the removal of the mind stone from Vision, to get him back up will require them to assemble him.
Avengers: Back in Time
Avengers: Earth's Mightiest Heroes
Avengers: Endgame?
It's my guess too, and it hearkens back to Stark who fired this all up. And it will fit with the thing I think they are going to do.