So apparently it is possible to unlock Super Saiyan God Super Saiyan Goku (henceforth refered to as SSGSS Goku for the sake of my sanity) in this game.
As seen in this friendly yet obnoxious video: http://youtu.be/VxnA6IUX1oI
I'm posting from an ipad so I'm not able to imbed the video yet, but basically if you have the demo of Extreme Butoden installed on your 3DS, the full game can import the save game and unlock SSGSS Goku as a playable character. When I try to do this, the import option shown in the video does not appear. Now he's using the japanese version of the game, so I'm assuming that's the issue. But it has to still be possible, right?
I fear no one else is playing this game and I may simply go mad wondering.