Avengers: Infinity War is set to push the boundaries even further in terms of scope, and if you have a much larger film, chances are you need even more characters to make it all work as planned.
In an interview with IGN's Terri Schwartz, Writers Christopher Markus and Stephen McFeely were asked if the movies would feature separate teams in Infinity War Parts 1 & 2 since the forming of a Secret Avengers-like group is teased in Civil War, which would also make the teams a manageable size for each film. McFeely took the first swing at describing how they are approaching the sizable amount of people in the film.
"When outlining it we certainly had those conversations. I mean in the same way, that in Civil War not everyone has the same amount of scenes or lines, I think you can assume that with so many characters we'll have to be as rigorous right? Where we say well these people will have sort of larger stories and these people will have smaller stories, and hopefully, they can flip in some cases. I know a few right off the top of my head that have a small part here and bigger part here."
Markus built on that, saying: "Yeah, the people in the background in one will come to the foreground in the second one. You know there will be moments where every last damn person who is still alive will be in the same room, and those are just a nightmare to write because Marvel, being very good about hiring very good actors who like, the 15th person there has two Oscars, and it's like oh my god. So yeah, it's crazy."
It will be a tall order, especially if Guardians of the Galaxy Vol. 2 introduces anyone else to the mix by then. Seeing how they handled it in Civil War though bodes well for both Infinity War Part 1 and 2.