Avengers: Endgame was a movie with so many characters that to juggle them all on the screen was no east feat. Captain Marvel had only just made her debut when Avengers: Endgame arrived in theaters and while she largely took a back seat to the legacy heroes in that movie, when Brie Larson's character does make her big arrival in the film, it's certainly done in a way that she gets noticed.
Having said that, it turns out that the way Carol Danvers could have looked when she arrived during the final battle of Avengers: Endgame could have been quite different. Marvel Studios artist Andy Park recently revealed a concept he drew that would have drastically changed the helmeted look for Captain Marvel, that didn't end up getting used. Check it out.
The idea, according to Andy Park on Twitter, is that the Russo Brothers wanted to change up Captain Marvel's costume in some way to show the jump in time that took place between the beginning of the film and the rest of the story. His idea was to go with a version of the Captain Marvel mask that kept the character's hair free, rather than the full helmet we saw in the Captain Marvel movie.
In the end, the look wasn't used, in fact we don't really see the old version of the helmet either. Carol Danvers seemingly decides to just leave the helmet behind entirely. It makes sense. By this point in the movie, the passage of time has been made quite clear, and Brie Larson's new haircut shows the passage of time on its own. The helmet, which is really more of a mask in this look, isn't necessary, though it is too bad it wasn't used, it looks pretty cool.
Figuring out how to handle the whole "passage of time" thing for Captain Marvel was a bit trickier than it was for other characters, because Brie Larson actually filmed her scenes for Avengers: Endgame before she got around to making Captain Marvel. Time sort of goes in the wrong direction here. As such, it was a bit more complicated to figure out how they would have wanted the character to look in Endgame when decisions about how she was going to look in Captain Marvel hadn't been decided yet.
Perhaps we'll still get a chance to see this look down the road. We know that Captain Marvel 2 is a movie that's coming, even if we don't know exactly when. Maybe when it comes along we'll see this new helmet. It would be a shame to see the design go to waste.