From the press release with the trailer:
When the crew of the Enterprise is called back home, they find an unstoppable force of terror from within their own organization has detonated the fleet and everything it stands for, leaving our world in a state of crisis. With a personal score to settle, Captain Kirk leads a manhunt to a war-zone world to capture a one man weapon of mass destruction.And here's a link to the trailer with screen grabs for giggles.
Well, money had been on Gary Mitchell or Khan. I have a feeling it's neither.
First off, we're told the character is canon (that is, he's in the original Star Trek Universe). But, in the new time line, Gary Mitchell has already been killed in the comic (and the comic has been declared canon, unlike the Original Animated Series). Although, without seeing how they did it in the comic, I don't know if it's possible for a demigod to return. Gary certainly would be "a one man weapon of mass destruction" and might be back to settle however he was killed. Gary would be able to bring down the fleet.
But, that would mean that the movies would rely pretty heavily on external material. Unless there's a flash back scene, but I have to admit even among fans of a certain age, not everyone remembers Gary Mitchell. So that would have to be one hell of a long flash back to bring everyone who hasn't read the comics (raises hand - hey, I have a life, okay, it's kinda busy right now) up to speed.
It could be Khan, which would fit the teaser about the homage to ST II in the Japanese version, which is slightly longer. It would also fit the spider jumpiness and the personalness of the violence. But then, Khan hasn't been discovered yet (although in the alternate timeline that part may be taking place with another ship, which Khan might have been able to take over). So he hasn't been stranded on Ceti Alpha V, it hasn't been blown into Ceti Alpha VI's orbit, so Khan's personal vengeance against Kirk hasn't developed (although he certainly carries a grudge against humanity which defeated him in the Eugenic Wars). But Khan is not "from within their own organization."
Trelane (the nascent Q)? Probably not. Again, not from within, and he would want play things.
Lazarus, Charley-X? The same thing. They're not from within. Captain Garth (Whom Gods Destroy)? Although certainly from within, and crazy, but not in that manner.
So, who could it possibly be? Well, I could see a path where it could be Khan, but I have a better answer, especially with the line in the Japanese extended trailer,"Is there anything you would not do to protect your family?"
It's Sybock, Spock's brother. The emotional Vulcan from the oft forgotten Star Trek V, Silliness at the Core. In the original timeline, Sybock takes the path of peace. As that's one path Vulcans can take. However, remember, Vulcan's nearly destroyed themselves in continuous wars until Surak taught them to revere logic and bury their emotions. With the destruction of Vulcan, Sybock may choose a different path from the history of Vulcan.
Although I'll put a side bet on Khan.