It's learned what sort of powers the Scarlet Witch will have in The Avengers 2.
Elizabeth Olsen talks to Total Film with mention that she can cast "hexes."
I just love Scarlet Witch. She is a messed up lady. She can tell you where an object has been, she can tell you what your future is, she can connect with the dead and people from other universes, and she's the only person in this universe who's capable of doing that.
Aaron-Taylor Johnson also adds that Scarlet Witch is his character's emotional anchor.
His sister really is his guidance. He's very over protective [of her] physically, but emotionally she's the one who looks after him.
It's also stated that (as shown in the Captain America 2 post-credit scene below), Scarlet Witch and Quicksilver are being held captive by Baron Wolfgang von Strucker at a remaining Hydra cell, and that at one point during the movie they will be recruited into the Avengers Initiative and join the fight against Ultron.
"The Avengers: Age Of Ultron" hits May 1, 2015 directed by Joss Whedon starring Robert Downey Jr., Chris Evans, Chris Hemsworth, Scarlett Johansson, Mark Ruffalo, Jeremy Renner, Samuel L. Jackson, Elizabeth Olsen as Scarlet Witch, Aaron Taylor-Johnson as Quicksilver, Paul Bettany as Vision, with James Spader as Ultron.
Head on over to the Cosmic Book News Avengers movie hub for more.