Needless to say, this story will be LOADED with spoilers for Avengers: Infinity War. If you are one of the few who has yet to see the latest Marvel movie, back out now. Come back after you have seen the movie in its entirety.
Because Avengers: Infinity War and Avengers 4 were filmed back to back, for the most part, there were a lot of rumors that Captain Marvel (Brie Larson) might show up in THIS section of the sprawling saga -- knowing that she'd also have her solo movie to fill in some gaps when Captain Marvel opens in March 2019. Though, while Carol Danvers was hinted at when Nick Fury (Samuel L. Jackson) sent her a long-range message, we didn't actually SEE Captain Marvel in the end credits sequence... for good reason. The Russos were asked in an interview if they ever considered showing Larson in costume in the end-credits scene for Avengers: Infinity War, and they said:
Joe Russo: No, we want to save her reveal.
Anthony Russo: We also wanted to, it was very important to us to commit... we wanted to commit to this ending very hard. We didn't want to go past the ending very much.
Joe Russo: And we considered not doing any tags. For that reason. Then we thought maybe it was too brutal. Everything's about trying to find balance.
Instead, we get a shot of her logo on the communications device that Nick Fury uses to message Carol Danvers... wherever she may be. This will be explained, we imagine, in the Captain Marvel movie. And then, it's assumed, that the hero will play a big role in bringing balance to Thanos' evil plan in Avengers 4. So, when MTV asked the Russos on the Happy Sad Confused podcast if Carol Danvers would be significant to Avengers 4, they dodged the question slightly and elaborated:
Joe: I mean, all of these characters are. It's hard to talk about the next one. We're going to try to protect the secrets of that one the same way that we did on this one.
Anthony: She will be a part of the MCU at that point. And part of the promise of these movies is that they are a road forward for all the films.
This is true. Though, as the directors are fond of saying, Avengers 4 will be the final chapters of a book that has been written for 19 movies so far, and more books will be written, but this will be actual closure for several key members. Which is why we saw Spider-Man (Tom Holland), Black Panther (Chadwick Boseman), Doctor Strange (Benedict Cumberbatch) and the Guardians disappear in this movie, and the core Avengers get left behind. Maybe those heroes are being saved for what comes next?