Carol Danvers has been a major player in the Marvel Comics universe for nearly 50 years, and in early 2019, she'll finally make her big screen debut in Captain Marvel, the Marvel Cinematic Universe's first superheroine-led movie. Captain Marvel is also serving as the penultimate installment of the franchise's Phase Three, with the still-untitled Avengers 4 wrapping up this period of the MCU a few months later. Because of that short period between the two releases, could we see Brie Larson's Carol Danvers participate in the fourth Avengers story after her first live action appearance? For right now, the answer is a strong 'maybe.' Marvel Studios president Kevin Feige recently said the following:
Really, the focus now is on delivering Captain Marvel and then bringing Captain Marvel's story into the finale of everything we've started thus far.
Marvel hasn't publicly indicated yet if Captain Marvel will show up in Avengers 4, but Kevin Feige's quote indicates that at minimum, the mythos of Carol Danvers' story will play into latter movie. However, before leading into Feige's quote, Indiewire states that Brie Larson will appear in Avengers 4. Until Feige or another Marvel bigwig definitively states that Carol is participating in Avengers 4, this is not 100% official, but it would seem the chances of her making an appearance are likelier than not.
It was revealed at this past San Diego Comic-Con that Captain Marvel will take place in the 1990s, approximately a decade (or more) before the modern MCU era. As Carol's origin story unfolds, we'll see her fighting the shapeshifting Skrulls, as well as share screen time with a younger Nick Fury, who at this point still has two working eyes. Because Captain Marvel takes place at least 20 years before what goes down in Avengers 4, the big question is where has Carol been for all these years? If she does indeed appear in Avengers 4, then we'll finally have that answer, as well as learn how she still looks the same after all these decades. Carol's energy powers will also be most handy against whatever threat the other MCU heroes are dealing with, be it Thanos again or someone else.
Along with spotlighting one of Marvel's most prominent super heroines, Captain Marvel will also help expand the MCU's cosmic corners. While it's highly unlikely that Carol Danvers' movie will be as intergalactic as the Guardians of Galaxy installments or Thor: Ragnarok, Kevin Feige stated that the tale will delve into the mythology of the Kree-Skrull War. It's also rumored that Mar-Vell, who was the original Captain Marvel in the Marvel comics universe, will appear in Captain Marvel, which would be fitting since the Kree hero was directly tied to Carol's origin story on the printed page.