It came to light shortly before the release of Avengers: Age of Ultron that Captain Marvel was going to be revealed at the end of the movie as a member of The New Avengers. As we now know, this never came to pass. So why was she cut?
“Very, very early in development, there was a notion that there could be a ton of new people,” Marvel Studios producer Jeremy Latcham told guests at an Avengers: Age of Ultron home entertainment release party. “And then it was like, ‘We haven’t really introduced them. We don’t know where they’re gonna come from’. Joss kind of did not love that idea… It was an early discussion. Then it became, ‘We’ll just see Captain Marvel.’ Then that felt weird. Just to have one new person.”
“The truth is, it didn’t seem appropriate to have this new person in a new costume just literally come out of nowhere at the end of the story,” Kevin Feige added. “It would have been a disservice to what, by the time this movie was coming out, people knew was coming anyway… Part of it, too, is that Cap says, ‘They’re not the ’27 Yankees.’ If Captain Marvel is there, what are we saying about her? There’s a notion that they — Wanda and Vision and, I think to a lesser extent, Falcon and Rhodey — need to learn what it means to be a team.”