Here is Joss Whedon's interview for Age of Ultron:
http://www.comicbookresources.com/?p...ticle&id=57857
In terms of new characters, there are plenty of running theories as to where Quicksilver and the Scarlet Witch got their powers -- with the shortest odds on them being Inhumans. However, the source of their powers may not be as simple as that.
"Baron Struckers been doing experiments, and hes got the scepter, and hes been using alien
tech
to do them," Whedon said. "Its kind of where I landed with that. But look for an exciting ret-con in 'Avengers 6!'"
Of
course
, many have already made the comparison of Scarlet Witch to some of Whedon's other powerful, but damaged characters -- like a ultra-powerful Willow in "Buffy the Vampire Slayer" or fan-favorite "Firefly" character River Tam.
"Well, you know, 'strong but damaged by power' describes every person in this movie," said Whedon. "It may, in fact, describe what the movie is about. You know, the more power that we have, the less human we are. Her damage pre-dates her power, and these kids theyve had a rough history. Is she in an idiom with which I am comfortable? Why, yes sir, she is.