After the online tidbits already revealed, the full
Entertainment Weekly article with the SDCC special reveals even more insight into the upcoming
Avengers sequel, including an uncut version of that team picture, revealing the person on the left side as Thor in his civvie clothes.
“So to me, Iron Man was like a returning verteran going back to the nuts and bolts of what was always righteous about who he was,” says Robert Downey Jr.
“He was never a guy who didn't get his hands dirty. He was a tinkerer. He’s a mechanic.” It's also revealed that Ultron will be an "all-seeing, all-knowing captain of the Iron Legion, a planetary force of robotic beat cops that resemble blue-and-white versions of the Iron Man suit."
About the twins Wanda and Pietro Maximoff, aka Scarlet Witch and Quicksilver, Joss Whedon says,
"They're on Team Ultron, which makes things really hard for the Avengers because all of a sudden they're dealing with powers that they're not used to. While Quicksilver can move at lightning speed, the Scarlet Witch can harness magic and telekinesis.
"It's not that she's insane, it's just that she's overly stimulated," Elizabeth Olsen explains. Whedon also considers a fourth member of Team Ultron in the Vision, a "synthetic, superpowered human desigened by Ultron to show he has the power to create life, too." That casting of Paul Bettany for this role is not coincidental as Whedon confirms but doesn't give any details. It's safe to assume though that Ultron uses J.A.R.V.I.S' consciousness for spare parts in his Vision-ary experiment.