Rumors have circulated recently that Marvel has already cast its (female) Captain Marvel, and that the new film The Avengers: Age of Ultron will conclude with a scene in which Captain Marvel is introduced to audiences as a part of the new and improved Avengers team. There’s no word yet on whom Marvel has cast in the role (despite lots of speculation), but movie-news site Latino Review has some more information about the character’s place in upcoming films:
RT! HOT #MARVEL #RUMOR ABOUT #CAPTAINMARVEL #SPOILER Apparently, from what I'm being told, the rumor is that the studio has cast the role of Carol Danvers & keeping it top secret. I'm also being told we will first see her in #AVENGERS #AgeofUltron as originally written in previous drafts of the screenplay. In terms of the standalone film, the Marvel brain trust has blocked out the plot & story with the intention of bringing an established writer to write the script. Comic writer Kelly Sue DeConnick wanted to take a crack at writing the screenplay but I'm not sure if she got the gig. Also, I'm told legendary comic writer Jim Starlin, who has a rich history with Captain Marvel is aboard the project as a consultant. All of the above is #UNCONFIRMED so take with grain of salt until further notice but it's within the realm of plausibility.
Source: Latino Review