So far, the Marvel Cinematic Universe’s Ant-Man movies have been as small in scale as the title hero himself, with director Peyton Reed and star Paul Rudd more of focused on telling stories set in a much more confined corner of the franchise than the typical planet-saving adventures that the rest of the Avengers usually find themselves caught up in.
However, Scott Lang’s increased role in Avengers: Endgame could be an indicator that Ant-Man is set to become a much more important cog in the machine, especially when you consider the constant rumors that the threequel will start laying the groundwork for the Young Avengers, with Scott’s daughter Cassie having been a key member of the team in the comic books under the alias Stature.
Another popular line of speculation is that Ant-Man 3 could also serve as the catalyst for bringing the Fantastic Four into the franchise using the Quantum Realm, which as in-canon pseudoscience presents an almost limitless number of storytelling opportunities that could be easily explained away by a few lines of dialogue and some exposition.
The latest theory making the rounds is that the Fantastic Four could appear in Ant-Man 3 via Overspace, which is essentially the opposite of the Quantum Realm, and is also accessed through the use of Pym Particles. In the comics, the Fantastic Four have found themselves stranded there before, which would both explain why nobody in the MCU besides possibly Hank Pym had ever heard of them should they appear, and also avoid the need for a full-blown origin story.
As ScreenRant explains:
It would be pretty easy to use Overspace to introduce the Fantastic Four. Imagine Mr. Fantastic as a contemporary of Hank Pym’s, who also experimented with Pym Particles but was interested in discovering Overspace by increasing mass rather than shrinking to enter the Quantum Realm, and who unfortunately became stranded there. This wouldn’t necessarily mean Reed Richards and the rest of the Fantastic Four were old, incidentally; time flows differently in Overspace, and in an even more complicated way to the Quantum Realm. In fact, time appears to operate differently every time you visit it. The first time the Fantastic Four and Spider-Man headed there, they spent hours exploring and returned home to find mere minutes had passed; the second time, they spent hours there again, but missed two months of life on Earth. In fact, Mr. Fantastic deduced the passage of time was accelerating exponentially.
Trapped in Overspace, the Fantastic Four would have had no real sense of the passage of time on Earth, perhaps only believing they’d been there for a few weeks at most. In the “real” world, though, decades would have passed – and Hank Pym, having successfully brought his beloved Janet Van Dyne back from the Quantum Realm, could now have decided to try to bring back some other long-lost friends as well. The Pyms’ initial breaching of the threshold to Overspace would serve to “reset” the clock, meaning the relationship between time in Overspace and on Earth would begin slowing down again. It would be a neat way to bring the Fantastic Four into the MCU, and it would avoid repeating previous approaches taken by Fox.
Peyton Reed is a known fan of the Fantastic Four, having pitched a movie to Fox nearly 20 years ago, and if he was given the opportunity to bring them into the MCU, then you can guarantee that he’d grab it with both hands.