Variety has word from actor Andy Serkis that along with consulting with Mark Ruffalo for his motion-capture scenes as The Hulk in Avengers: Age of Ultron. That he'll also have an unnamed role in the film as well. Considering his high-profile taking lead roles in films such as King Kong, Lord of The Rings, Rise/Dawn of Planet of The Apes and Star Wars: Episode VII, we should expect a big part for Andy.
"The Imaginarium is the performance capture consultant, and I’m playing a role,"
"I’m not at liberty to mention. But it’s all the same to me. I’ve never drawn a distinction when playing a role, whether it be live action or performance capture. Acting is acting. It’s just basically what you wear to the set that’s different."
I assume that this character could be more labor intensive, than say the voice work that Bradley Cooper and Vin Diesel did for Guardians of The Galaxy. Considering he's basically the best performance capture actor working today (here's hoping the Academy eventually makes performance capture a category), I doubt this is the motion-capture work for Thanos or Ultron. I have a strong feeling he'll get his own character in the film, likely setting-up Avengers 3 or future Marvel films.
KANG: Another Marvel cosmic villain that could be teased at the end of Age of Ultron (similar to Thanos in Avengers) is Kang The Conqueror. Although Kang is from the future, placing him among the ranks of Thanos wouldn't be too difficult. Marvel has already placed cosmic villains such as Ronan The Accuser and The Collector into the service of Thanos, so it's possible other villains like Kang could become his pawns as well.
I'm not sure if Marvel is ready to throw the villain into the spotlight, but setting him up for Avengers 3 could make a lot of sense. Yet, we know that Marvel is changing the origins of Ultron, having him created by Kang, might also be a new angle for the villain. Having Serkis do a cameo as Kang would allow him plenty of time to make more Star Wars and Apes films, before taking a bigger role for Avengers 3, which is expected to be released in either 2018 or 2019. Kang would also make a great villain for future installments.
The time-travelling aspect is apart of the original Age of Ultron storyline, and if the film does end-up using that theme. Having a character like Kang, that possesses time-travelling abilities in the MCU could be a way to allow that to happen. Or, at the very least keep the time-travelling aspect in place, somewhat.
GORILLA MAN: Considering how much attention Rocket Raccoon is getting, it wouldn't be much of a stretch to see another animal mo-cap character join the MCU. Mainly, Gorilla Man one of the Agents of Atlas, the team also includes SHIELD agent Jimmy Woo and Namor's cousin Namora. The gun-wielding Gorilla Man is another heroic animal from the Marvel universe, and seems like an easy character to assume Serkis could play. Having played two iconic apes in the past already, with Caesar (Rise/Dawn of The Planet of The Apes) and King Kong. Of course, Gorilla is entirely different than those previous roles, which would mean a brand new ape character for Andy to play with. Plus, getting to do more action sequences as well.
ABOMINATION: There has been more than a few teases that we could see the return of The Abomination, and a massive battle between these two could result in major civilian causalities. Leading to the eventually plot points that start-off the Planet Hulk story. I actually liked Tim Roth's Blonksy, but hated the design of Abomination. Perhaps, another redesign is in order and possibly a recasting. Since Ruffalo is now Banner, we could see other Incredible Hulk characters recast with new actors. It would also be great to see Andy play a straight-up menacing villain.
RED HULK: We strangely haven't see William Hurt return as General Thunderbolt Ross. A possible sign that both Hurt and Liv Tyler might be getting recast for future films. I think that Serkis is able to age himself up enough to pull-off both the General and Red-Hulk versions of Ross. Apparently, Red-Hulk was expected to be a feature player on the axed ABC series. It's not hard to imagine Marvel wanting to use him in the films instead. Marvel has also been setting-up the "Hulks" with their animated series The Agents of SMASH. I'd actually love to see Andy play characters like this, ones with a mix of both live-action and CGI performances. Plus, Andy rocked a great moustache in King Kong.
SILVER SURFER: Currently, the rights to this cosmic hero are at Fox. However, at one point Marvel was trying to make a deal with 20th Century Fox to regain the rights to both Surfer and Galactus. The studio was trying to include the characters in the recent production of Guardians of The Galaxy. At the moment Fox isn't ready to move forward with old plans to make a Silver Surfer film. At best, he'll end-up another secondary character in the new Fantastic Four franchise. I'd personally love to see what someone like Serkis could bring to both Norrin Radd and The Surfer. It's extremely unlikely we'll see the Silver Surfer in Age of Ultron, but he's a character Serkis could really give dimension to.