I read an interesting Avengers 4 time travel theory.
Before the main theory, there's a couple of theories about how time travel may work:
- Either strange sent the timestone into the future while they were fighting Thanos on Titan for the snap survivors to use (and then send back to Strange when done)
- Or, they end up using a Time Vortex in the Quantum Realm
Anyways, the theory is that during the battle of New York (Avengers 1), they basically have a known location of Thanos sans gauntlet (through the wormhole). If they can get back to 2012 and get through the wormhole without interfering with the rest of the timeline, the OG Avengers can take the fight to an unpowered Thanos. This could also lead to Tony's vision from
Age of Ultron coming true (all of the Avengers dead on the stone steps in space).
If they could pull it off without altering the actual battle with their past selves, the rest of the MCU timeline (at least on Earth) would play out the same (dark world, ultron, civil war, etc).
The only problem i would see is that Thanos plays heavily into GOTG. It is possible that Ronin has already been tasked with finding the Power Stone, and since we know that he ends up betraying Thanos anyways, that story should mostly remain intact.