movie ties into Avengers 4 in a fairly big way.
In the meantime, Avengers 4 is slated to arrive in theaters on May 3, 2019 while Spider-Man: Far From Home will come shortly afterward on July 5, 2019. Set photos have shown Scott with Captain America and Iron Man, so it's safe to assume he will escape the Quantum Realm in time to save the universe in the next movie. Or maybe he even learns about Thanos and attempts to warn the Avengers of his presence early on in the MCU's running timeline? Mar-vell has a history with Thanos in the comics, so his connection to Carol Danvers should prove important.
The mid-credits scene is the one that has the most significance to the future of the Marvel Cinematic Universe, because it shows Scott Lang fiddling about inside the Quantum Realm, which the film tells us is a very risky place.
The Quantum Realm was originally described by Hank Pym as "a reality where all concepts of time and space become irrelevant as you shrink for all eternity". Scott, meanwhile, is stuck in the Quantum Realm. Evangeline Lilly has even noted that the new territory "does open a whole entire new multi-verse to enter into and play around in". But the fact that such an obscure character can carry a franchise is proof that Marvel can ensnare viewers with even its most peripheral characters.
As such, the MCU has sufficiently established that an endless amount of different planes of existence are present at any given time and can conceivably flow into one another.