That's what I think Feige and Marvel are planning for 2018. I think they're going bigger than anyone thought with these films and aren't just planning for the third Avengers film to be strictly an Avengers film, but a film that crosses them over with the Guardians of the Galaxy, and possibly other properties that will be in phase 3 like the Inhumans. Avengers 2 is about going deeper into the team, pushing them and teaching them how to actually be a team. After that though, they will be a puzzle piece in a much bigger canvas. There is a reason Marvel is going into a completely different branch of their universe with GotG that doesn't appear to seg into Avengers at all, and that is because it is meant to be a separate arm. This is like the difference between Iron Man, Thor, and Captain America except on an even bigger scale. BUT, the main thing tying these films together is Thanos, and that will be what brings them together as well. As for "branding", so to speak, instead of being "Avengers 3: The Thanos Imperative", it would be, for example, "Marvel's Annihilation: The Thanos Imperative". This way you're not undermining the Avengers in an Avengers movie, they'd just be a piece of a bigger puzzle, as I said before. It will take more than the Avengers to defeat Thanos, just like it will take more than just the Guardians as well. So essentially, this will not be a movie of any specific property, it will be a complete Marvel crossover event movie encompassing multiple properties. So the restrictions that they place on themselves in standalone films, like not allowing characters from other franchises to make random cameos and the like, will be out the window. By that I mean, we could see characters from the TV shows making quick appearances or something and it wouldn't feel at all out of place, as the structure behind the movie in the first place is that it's a pure Marvel crossover event film. This film would basically be the culmination of the 10 years of set-up they started with the first Iron Man movie, and they would pay homage to everything they've done. That includes maybe just showing quick glimpses of what the TV characters are doing when some seismic event happens. Cameo stuff. But how do you fit so many characters into one movie? Well, I think it would be awesome if they were to try their hand at the Deathly Hallows split model, with the first part of the movie being released in 2018 and the second part in 2019. But, that's thinking way too far ahead on top of thinking too far ahead. My point is, it's possible for them to do this type of mega crossover without it imploding on itself. This is the "merging of the brands" I think Vin Diesel was talking about that is "way, way off".