This has pretty much been teased again in a new interview with the studio head by Bloomberg Businessweek. Here's a snippet from that interview.
Gunn freezes a frame of an imposing-looking villain any serious comic book fan would recognize instantly. He sits on a rocket-powered throne. Feige sees something on the screen that he doesn’t like. The evildoer needs to be farther away in the frame so he looks more imperious, he says.
“I don’t know,” says Gunn. “I think it’s going to look cool, man.”
“You just don’t want him to feel petty in that way,” Feige says. “I think it’s a fine line.”
“How do you think it comes off as petty here?” Gunn says.
“He’s so damn close,” Feige says.
“Yeah,” concedes Gunn. “I think I’m going to have him floating in space.”
Feige is concerned about the throne, too. He points at the base. “Those don’t need to be rockets,” he says. “Maybe gravity disks?” Feige says he’ll check back later.
In the hallway he extracts a pledge [from Bloomberg writer Devin Leonard] not to name the bad guy. “That could not be a bigger spoiler,” Feige says.
The tease seems to imply Thanos, who was seen on a throne in his brief moments in The Avengers, However, the villain MODOK also sits on a rocket chair that could have been perceived as being a throne by Bloomberg writer Leonard. Regardless, it sounds more probable to be Thanos since his general, Ronan the Accuser, is the main villain of the film and who is pursuing the Guardians.
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