Marvel has been pretty coy about who would play the Scarlet Witch in Avengers: Age of UItron. Samuel L. Jackson, not so much — especially after he told The Wall Street Journal that Elizabeth Olson is his new cast-mate.
"I don’t think we begin shooting before March of next year. I know we're shooting in London, that James Spader is Ultron and going to be the bad guy, and that we added Ms. [Elizabeth] Olsen [who will play the Scarlet Witch], but I don’t know what she’s doing, if she’s on the inside or the outside. I haven't seen a script."
The brackets are the WSJ's, so Jackson didn't specifically confirm Olson is playing the role, but since Olson has been the rumored frontrunner for the role and the Scarlet Witch is the highest profile new female character in the Avengers sequel that we know of, I think we can consider those brackets accurate. Although if Joss Whedon wants to make her the Wasp, I'd be down with that, too. (Katee Sackhoff still needs to be Captain Marvel, though.)