According to Marvel Studios President Kevin Feige, the Quantum Realm becomes "really important" to the Marvel Cinematic Universe moving forward.
"I think it's one of the fun things about the comics that allow you to explore entirely new terrains," Feige told ScreenRant. "And we've hinted at it now in numerous films and it's untapped, primarily untapped potential."
As Ant-Man and The Wasp showed, the Quantum Realm offers a lot. Ghost got her powers from it, as did Janet van Dyne when she was forced to survive there for decades. The film also offered a glimpse of a city within the Quantum Realm, which proves there is a lot more there to be explored. The prevailing theory is that the Quantum Realm will play a role in both Captain Marvel and Avengers: Endgame.
Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Chadwick Boseman, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie. The film arrives April 26.