There was a time when the prospect of a SHIELD movie was being seriously bandied about (before The Avengers hit theaters), but at this stage it's safe to say that's highly unlikely to happen. Instead, Marvel's Agents of SHIELD TV series will offer a more intimate look at the organization's inner-workings - with the occasional guest star appearance from a member of the larger Marvel Cinematic Universe - while the sequel Captain America: The Winter Soldier will revolve heavily around the top dog agents at SHIELD (including, Steve Rogers).
The Winter Soldier storyline picks up in real-time, i.e. two years after Loki and his Chitauri army invaded Manhattan, with Cap/Steve (Chris Evans) and Natasha Romanoff/Black Widow (Scarlett Johansson) now partnered together and fighting various threats which have cropped up since the world discovered the existence of superheroes (beyond an eccentric billionaire playboy in a high-tech flying armored suit, that is).
Speaking of heroes in flying suits: Anthony Mackie costars in The Winter Soldier as Sam Wilson/Falcon, who frequently collaborates with Steve and Natasha on their dangerous missions around the globe. During a recent discussion with MTV, Mackie was keen to emphasize that Falcon isn't a sidekick to the pair of Avengers who're at the center of the action in the Captain America sequel:
"It's interesting because a lot of people equate it [Cap and Falcon's relationship] to Batman and Robin, but the reality of it is it's more of a working relationship, a respect relationship as opposed to a leader and follower. The three of us [Steve, Sam and Natasha] work really well together."
Mackie's comment here compliment the statements made by his costar Johansson a couple weeks back, when the actress spoke about the key importance of the Cap-Widow relationship and suggested that the pair are on equal footing in the film. Winter Soldier directors Anthony and Joe Russo have also claimed that "the journey that [Cap and Widow] go on together is the heart of the movie,” while Mackie's description of Falcon suggests he'll be another essential SHIELD agent in the story - one who (at the least) gets equal/more screen time as a supporting character like Samuel L. Jackson as Commander Nick Fury.
MILD SPOILERS AHEAD!
Having said that, Mackie also confessed to MTV that Falcon's role in the Winter Soldier narrative - devised by Captain America: The First Avenger screenwriters Christopher Markus and Stephen McFeely - isn't as front-and-center as he'd originally been led to believe:
"They sold me that I was the second lead in the movie, so there's a point where Cap gets hurt, and [I] do everything for Cap. And I get the script, and... that's not true. I get hurt, not Cap!"
Mackie has confirmed that he signed a standard multi-picture contract with Marvel, which means it's possible that Winter Soldier will primarily serve as the introduction to Falcon (a la how Iron Man 2 incorporated Black Widow into the MCU); meaning, the character might not feel like a sidekick to Cap in the sequel, but he'll still only get as much screen time as one.
On the other hand, by bringing Falcon into the MCU universe now, that could lead to Mackie having a bigger role in Captain America 3 during Phase 3 of the MCU (note: a third Cap movie has not yet been officially confirmed for Phase 3) - perhaps, following a (brief) appearance in The Avengers: Age of Ultron, at the conclusion to Phase 2?
What are you theories about the role that Falcon will serve in the MCU, beginning with his introduction in The Winter Soldier?
Thor: The Dark World opens in theaters on November 8th, 2013, followed by Captain America: The Winter Soldier on April 4th, 2014, Guardians of the Galaxy on August 1st, 2014, The Avengers: Age of Ultron on May 1st, 2015, Ant-Man on July 31st, 2015, and unannounced films for May 6th, 2016, July 8th, 2016 and May 5th, 2017.