Agreed. Or, simply witchcraft, in SW's case. (I believe that it would be easier for general audiences to understand Wanda by her namesake: "Oh, she's a witch, like in Charmed. I get it.") A speedster's skillset would be easy enough to pick up on, too, but you'd probably need some pseudo-scientific reason to explain the source of Pietro's power. Either way, this might be a good time to remind folks who have doubts that Wanda & Pietro never came to the Avengers with any solo backstories of their own. Like plenty of Avengers, they were more or less introduced in the team title, so it makes more sense for them to get their origins told in an Avengers movie rather than trying to parcel them out to solo films.