So after seeing Endgame, here are my thoughts on the timeline(s) moving forward. /u/pixelcraftables posted
this over at /r/marvelstudiosspoilers and I largely agree with this. I would say the prime MCU timeline has stayed entirely intact from what was shown in the movie; the scenes set in the 70's, The Avengers in 2012, Thor: The Dark World in 2013, and the events on Vormir in 2014 can all be considered canonical. The 70's scene obviously could have just happened and we haven't seen it before, just as any other flashback scene happens in any other movie; Tony takes the space stone and within seconds, Steve returns from the end of the film and puts it back. The sequence from Thor: The Dark World could have happened off-screen; Rocket takes the reality stone from Jane as Thor talks to Frigga and grabs Mjolnir and within seconds, Steve returns from the end of the film and gives the reality stone back to Jane and puts Mjolnir back. Natasha and Clint go to Vormir in 2014 and retrieve the soul stone and within seconds, Steve from the end of the film returns it.
The scene set in The Avengers in 2012 is a little more complicated, but I still feel as if this could be considered canonical. Banner retrieves the time stone, an event that would have happened entirely off-screen in The Avengers anyway. The stuff that happens with the space and mind stones could have happened off-screen as well. Loki could take the space stone and could have been restrained by the Avengers again before the schwarma scene and Steve taking the mind stone makes sense within the timeline. Within seconds, Steve from the end of the film returns and puts the time and mind stones back.
The end of the film, with Steve returning to the past to stay with Peggy and returning as an old man, completes the loop, I feel. This way, all of the past continuity is at least somewhat maintained, which is a good thing because my biggest fear going into Endgame was that they would use time traveling in such a way that would negate the previous 21 films and make them all for nothing.
The events of Guardians of the Galaxy 2014, however, I feel is a completely new timeline; if Thanos and his army are brought forward in time and snapped before even Guardians of the Galaxy is over, the entire flow of events is kind of ruined. As far as I can tell, there is absolutely no way these events can happen in the prime MCU timeline. This is the only necessary branch in the timeline, I feel.
Regarding Spider-Man: Far From Home: so now I feel they can go two ways with this film: either it's set before Infinity War or they somehow explain that Peter and his entire class are able to stay intact and stay in the same education and grade level, despite five years having passed for the rest of the world. In the trailer, Peter's date of birth and the current year are blurred out intentionally, and now it will be interesting to see whether they insert 2017 or 2023 into the current year spot.
Regarding Agents of S.H.I.E.L.D.: this is by far my biggest problem with the film; it almost completely disregards Agents of S.H.I.E.L.D. while at the same time trying to bridge the gap between the ABC shows and the films by including Edwin Jarvis in the 70's scene. I'm trying to reconcile Agents of S.H.I.E.L.D.'s fifth season, which shows that time travel does affect the future, by saying that the White Monolith and the Quantum Realm are two different mechanisms of time travel, therefore they use two different versions of time travel (convoluted, I know, but I can't think of any other explanation at the moment). As far as season 6 is concerned, I'm assuming they will just try to explain it as the entire team got lucky from the snap; otherwise, it would almost seem like the entire show would no longer be canon and would instead be set in its own branch of the timeline, similar to the events of Guardians of the Galaxy in Endgame.
Regarding the Disney+ shows: I feel like these are all over the place now. Steve gives Sam the shield at the end of the film, setting up The Falcon and the Winter Soldier as the ongoing adventure of the present day Sam-Captain America, who teams up with Bucky. The Loki series has been described as a journey through the MCU's history, setting it in the past, which fits in with the fact that Loki was not revived by the Stark Gauntlet (at least not on-screen) in Endgame. WandaVision is the odd one out; according to Elizabeth Olsen, the concept art for WandaVision shown at the Disney+ shareholders event features Wanda and Vision in the 1950's. This, to me, says that the show begins with Wanda searching for a way to bring Vision back and ends up in the 1950's once again through the Quantum Realm. If this is the case, I'm hoping that they treat the series pretty similarly to Endgame because the 1950's is pretty open in the timeline right now and it might actually be very interesting to have a series set almost entirely in the past that wasn't known about yet.