The trailers for Ant-Man 2 even feature the craft that Hank Pym developed to explore the Quantum Realm, which seems like it would be really helpful to the original Avengers as they look for a way to go back in time.
Now that Infinity War has settled into theaters and Ant-Man 2 is on the way, the thirst for Avengers 4 knowledge is getting out of control.
In the first Ant-Man, Scott Lang successfully made it out of the Quantum Realm, much to the surprise of Hank Pym and Hope van Dyne.
Time travel seems to be the consensus of the majority of the Avengers 4 theories, especially after Doctor Strange’s sacrifice.