The mid-credits scene from Ant-Man and The Wasp has already leaked online, but there's one almost throwaway moment many seem to have skipped over which may hold the key to a major Avengers 4 plot point.
There is already some speculation that The Quantum Realm will factor into the time-travel story elements of the follow-up to Infinity War, and the Marvel sequel's much-discussed mid-credits sequence might just confirm it.
During the scene, Janet (Michelle Pfeiffer) warns Scott (Paul Rudd) to be careful he doesn't "get sucked into a time vortex" as he's about to traverse through the Quantum Realm. This, along with earlier comments about "time being weird" in the Miroverse, strongly imply that we'll be revisiting this time vortex in Avengers 4.
How, specifically? Well that's where your theories come in! But It's a safe bet that Cap and co. will call upon Scott's experiences in The QR as they attempt to reverse Thanos' universe-altering "snap" at the end of Infinity War.