MCU Phase 4: 10 Things They Must Address (And Not Just Forget About)
1. Time Travel Exists
Probably the biggest revelation to come post-Endgame is that time travel is a very real possibility. Yes, it creates alternate timelines, but it still does exist. Unless it's unclear, that's massively significant!
The implications for its existence are limitless. The Avengers used Pym Particles to go quantum and travel back in time to retrieve the Infinity Stones before the big purple space man could get them, so imagine what could be done by someone with different intentions. They could go back and stop a particular Avenger being born, or stop Howard and Maria Stark's deaths at the hands of the Winter Soldier, or actually get Keanu Reeves a part in this franchise. The possibilities are truly without end as a result of Endgame's time hopping.
Of course, this may cause conflicts in the timeline, or schisms with the universe, but that just creates more interesting problems to solve. The future of the MCU is bright, and it would be even brighter should they remember the simple fact that time travel exists now.
It shouldn't happen all the time, because then it wouldn't be as special, but to see it happen again like with Endgame's emotional Tony and Howard dialogue would just be incredible.