It appears as though actress Elizabeth Olsen has been perhaps confirmed for the role of Scarlet Witch for Avengers: Age of Ultron. As tends to be the case with Avengers news, the casting was inadvertently revealed by Samuel L. Jackson during an interview.
In an interview with the Wall Street Journal, he says:
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.
It has to be noted that the additional notes were added by the interviewer, and Marvel have not made any confirmation regarding the casting. They’re likely waiting for some kind of ‘Comic Con’ in a big city like ‘New York’ for such an announcement.
But! If Samuel L. Jackson says that Ms Olsen is going to be in the film, then you don’t argue with him. She’s definitely in the film – whether she is Wanda or not awaits confirmation.