Here's a short film synopsis from casting call information published by featurefilmcasting.com.
In "The Avengers: Age of Ultron" Loki is gone and the new villain will be the evil robot Ultron, who has the ability to keep upgrading his strength making him extremely fearsome. Tony Stark/Iron Man becomes the unwitting creator of Ultron. The brother-and-sister team of Quicksilver and the Scarlet Witch become the seventh and eighth members of The Avengers. Quicksilver has extreme speed, while Scarlet Witch can cast spells and has telekinesis ability. Black Widow and Hawkeye will be key figures in the film.
The article also goes on to say that Vin Diesel has not been confirmed for the movie and that Anthony Mackie is the front-runner (???) to play the Falcon.
Make of it what you will.