The other part of the MCU where The Quantum Realm may have a major impact is when Thanos makes his play for cosmic domination in The Avengers: Infinity War 1 & 2.
For those unfamiliar, The Infinity War involves Thanos gaining control of the Infinity Stones, seen as the major MacGuffin weapons in Avengers, Avengers 2, Thor 2, Guardians of the Galaxy, and Captain America: The First Avenger. Thanos unites the stones into The Infinity Gauntlet, a glove giving him power over time, space, power, mind, reality and the soul; basically, he becomes God. From that point on, the Marvel universe faces ultimate peril; in the comic books, more than a few heroes suffered brutal deaths by Thanos' gauntleted hand before the Mad Titan was stopped, and all evidence of his destruction erased.
In the MCU, Thanos will presumably achieve a similar stature of godhood, and word is that the original Avengers team won't show up 'til late in the fight to save the day. We don't know how such a scenario would even play out, but there are some conclusions to be drawn when you factor in The Quantum Realm.
It could be The Quantum Realm which ultimately bridges films like Guardians, Ant-Man and Doctor Strange's concepts of cosmic energy, science and magic, respectively, by being a channel for all those aforementioned forces. However, in a more ironic twist, it could be Ant-Man (the most mocked Marvel hero to date) and his unique powers that could be the real pivotal tool for defeating Thanos.
How Ant-Man Can (Help) Beat Thanos
Having been to the lost recesses of the Quantum Realm and survived, Scott Lang could access the abstract dimension in order to hide himself (or others) from Thanos. Besides hiding, Ant-Man and the Quantum Realm could be used as explanation for a big "twist" if the original Avengers seemingly get wiped from existence by Thanos. Instead of being vaporized, maybe they were just shunted into The Quantum Realm, until retrieved by Ant-Man (you get the idea...)?
Other fans are already buzzing with additional theories in our Ant-Man spoilers discussion. Marvel Comics has an entire mythos about personified forces of the universe that influence events, and some fans are already stating that the cosmic entity known as Eternity was spotted in the Ant-Man Quantum Realm sequence. Eternity is certainly a fitting representation of Hank Pym's description of being lost in the Quantum Realm - Eternity was also a key figure in defeating Thanos during the "Infinity Gauntlet" comic book storyline. So, in the Infinity War movie, Ant-Man could be the key to making contact with a cosmic entity like Eternity, helping to bring him (...or her?) into the conflict.
Other possibilities include Ant-Man using The Quantum Realm as a highway through dimensions - a highway that could somehow off-ramp him (and others) into the inner space of the Infinity Gauntlet itself, or one of the Infinity Stones. In the comics, Silver Surfer and Drax discover cosmic hero Adam Warlock inside the Soul Infinity Gem - so there is precedence for the gems (or Infinity Stones, in the MCU) being portals to other dimensions. All potentially accessible through the Quantum Realm, and therefore, accessible by characters like Doc Strange or Ant-Man.
Finally, more far-out theories include fan speculation that Hank Pym's wife Janet (first introduced during Ant-Man) could become the MCU embodiment of Eternity, due to her long time being sentient within the Quantum Realm. It would be a curve ball, no doubt - but that twist would admittedly tie together a lot of other MCU threads to make Thanos' defeat resonate with themes of each individual franchise - including Ant-Man proving himself a great Avenger, and Hank and Hope Pym finally being able to reconcile the loss of Janet.
Of course these are all just speculation and theory - let's hear your breakdown, or how likely (or not) these scenarios sound to you! Want to discuss the film without ruining it for others? Join our Ant-Man spoilers discussion - and look out for our Ant-Man Easters eggs and post-credits explanation posts in the days after release.
Ant-Man is in theaters; Captain America: Civil War – May 6, 2016; Doctor Strange– November 4, 2016; Guardians of the Galaxy Vol. 2 – May 5, 2017; Spider-Man reboot – July 28, 2017; Thor: Ragnarok – November 3, 2017; The Avengers: Infinity War Part 1 – May 4, 2018; Black Panther– July 6, 2018; Captain Marvel – November 2, 2018; The Avengers: Infinity War Part 2 – May 3, 2019; Inhumans – July 12, 2019.