We've been hearing a lot of Captain Marvel talk in the last couple of months, and her possible addition to the Marvel cinematic universe. Carol Danvers has the potential to be a leading super powered heroine, who doesn't have a villainous origin. Having a troubled past is something that Black Widow and Gamora both have in common. It would be nice to finally see a lead female character shake-off the love-interest cliche and given level footing with the rest of The Avengers. It's been rumored for over a year that Danvers would be joining the Avengers ranks for Age of Ultron. The size of the role (Carol Danvers/Warbird/Ms Marvel/Captain Marvel?) has never been explained or revealed.
I started taking the news seriously when TheDailyMail reported, that Ruth Wilson and Emily Blunt were candidates for the role, back in the fall of 2012. This was the same source that recently confirmed Paul Bettany would be playing Vision in Avengers: Age of Ultron. I have solid reason to believe these two might actually be the ladies truly in the running for the role. I know this might disappoint all the folks who were fan-casting Yvonne Strahovski and Alice Eve.
Emily Blunt has a notorious history with Marvel, originally signing-on to play Black Widow (Johansson set to play Scarlet Witch) in Iron Man 2, only to have Fox call-up her contract for Gulliver's Travels. Scarlet Johansson would fill-in for Emily, and has been the female face of the Marvel films ever since. This wasn't the only role offered to Blunt, she turned down the part of Peggy Carter in Captain America: The First Avenger (which went to Ruth's co-star Hayley Atwell from the series The Prisoner) and possibly Gamora (rumored only) in Guardians. If I had to guess why, the roles weren't large enough for her commit that much time. The Marvel contracts are quite lengthly, usually anywhere from three to six films.
Emily has been kicking-ass in her recent films Looper and Edge of Tomorrow, the latter has her killing a bunch of aliens. She's proven the ability to play strong and complex characters, which means she could easily support a Marvel franchise on her own. Having a well-known actress in the role of Danvers, is sort of a must, as Marvel can't gamble with hiring talent on a project like this. It's go big or go home.
Ruth Wilson had recently taken two high-profile Disney roles in films Saving Mr. Banks and The Lone Ranger. Not to mention, previously co-starring with Marvel actors Idris Elba in the amazing series Luther, and with Tom Hiddleston in short-lived series Suburban Shootout. I love Ruth Wilson to-death, but I'd rather see her take a different role in the MCU. Considering her working relationship with two Thor actors, seeing her play Amora The Enchantress or Brunhilde The Valkyrie in Thor 3 would be sublime. That said, Blunt has a track record of turning down Marvel roles and it could be up for grabs, if Emily walks again.
Joss Whedon would comment on using Ms Marvel, cutting down the character and teasing Tigra with a joke instead. Around the same time he was talking up the villainous twins Scarlet Witch and Quicksilver, hard to allow fans time to support Scarlet, if he was talking up Danvers (possibly a character with a smaller part in the film) as well. Let's not forget, Fox was going to include the mutant siblings in X-Men Days of Future Past. Joss needed to establish the twins as major players in the film. He's also not going to give everything away in an interview, keeping important elements and characters of the sequel a surprise. Baron Wolfgang von Strucker and Vision were recently revealed, which we weren't expecting to be added to the cast.
Whedon is supposed to be a "champion" of leading female characters, however, we don't have a franchise led by one (team-ups don't count). This is on the heels of Ant-Man (Wasp's inclusion only rumor at this point) kicking-off Phase Three in 2015. Along with mostly male-dominated projects like Doctor Strange, Inhumans, Black Panther and new Hulk film waiting inline for their own release dates. Yes, we have Jessica Jones finally getting her due, but that's television darling. Marvel could very well edge-out Warner Bros. by releasing a Captain Marvel film, before the studio can get their shit together to release Justice League or a solo Wonder Woman film. But, adding Carol to Age of Ultron makes sense and given the problems Joss has with her, he has the ability to fix those issues and create the cinematic version of that character.
Going even further than just a cameo, a rumor started circling that Marvel was strongly considering a Ms Marvel/Captain Marvel movie. We would later hear from THR, that Marvel Studios was working on a Captain Marvel script with an unnamed writer. I would assume it was coming from Nicole Perlman (Black Widow, Guardians of The Galaxy), who is apart of the Marvel screenwriters program (THR refers to the program). Perlman has a tendency to write the studio's female focused scripts (usually under the radar) and she is likely the writer spearheading the Captain Marvel script for Marvel.
There are plenty of entry points for Carol to get her powers, Age of Ultron is one and the Guardians of The Galaxy (or the sequel) is another. Ronan The Accuser (played by Lee Pace), a high-level member of the Kree Empire and will be seen in Guardians of The Galaxy, in the service of Thanos. I don't doubt that by the end of Guardians or even in the second film (expected for Phase Three), they could interact with Earth and it might involve Danvers (comic cannon suggests she'll get her powers by involvement of The Kree). The Kree connection would make things very tempting, to have her gain her powers within that franchise. It wouldn't hurt having another female team member either, it would also be a way to bridge Guardians and Avengers worlds without the need of Tony Stark.
Phase Three is quickly filling up with Ant-Man, Captain America 3, Thor 3 and possibly Guardians of The Galaxy 2 taking up the spots. There is still the expectation Marvel "might" make room for Doctor Strange. This means that Captain Marvel won't be ready until Phase Four. The Phase One characters will have their trilogies wrapped-up at this point, giving the new wave of heroes a chance to finally get their solo flicks released.