After Ant-Man and The Wasp was released in the US, many people including this site pointed out how the mid-credits scene could confirm one of the long-running theories about the Avengers 4 plot.
Now Peyton Reed has confirmed to The Huffington Post that the theory does have merit based on the credits scene:
“Based on the science that we’ve set up in the first movie and this one, I won’t rule out the possibility,” Reed said, “because, again, we are dealing with a time vortex. That could happen.”
He also confirmed that Scott Lang is indeed trapped in the Quantum Realm as his new suit doesn’t have the same abilities his one in the first movie did, meaning he can’t grow his way out:
“This is a new suit, so it really wouldn’t have the same growth that he had in the first movie … I would answer, ‘No, he does not have it.’ He can’t go to that well twice,” said Reed.
That means someone would have to discover Luis’ van on the roof of that building and free Scott from the Quantum Realm, which is part of that Avengers 4 theory.