That's what i thought whenever i first saw that commercial. He was still alive. Come on. Think about how they thought he was dead the first time. It's logical to think that he was revived again. It couldn't be a storyline covering the events before the first game like some have suggested for three reasons. (1) He seems somewhat older as far as his look in the teaser trailer goes, (2) he's remembering things that Vader said to him, not to mention his memory of Juno, and (3) though it seems impossible when you think about how powerful he was in the first game, that trailer made him out to be a lot stronger. His anger alone was enough to tear apart that corridor he was in. He wasn't even trying, duh.
Keeping in mind that it is most likely in future events, it'd be cool to think that he ran across Yoda in this one and gained more training. The memories he's having of Yoda also seem to point that way. I do agree somewhat with the prison idea, but i wouldn't know how that would work out with my theories. Maybe he was thrown out with the rest of the tash when they thought he was dead. He is then picked up by some slave ship or prison freighter which transports him to the arena he's at in the trailer (after they revive him ofcourse). He then escapes after having enough of getting by with being the sport for some collesium crowd to reunite with Juno and his friends from the rebellion. I'll bet Kota knows where to find Yoda, and THAT'S HOW HE GETS EXTRA TRAINING FROM HIM SINCE KOTA CAN'T USE THE FORCE ANYMORE! There's the connection.