Namco also rolled out their pre-order and collector's edition plans for the game. (For Europe, at least.) The "We Are Tekken" edition Tekken Tag 2 comes with an art book, a making-of documentary, and two soundtracks - the normal version and the "remix" album.
Players who pre-order the game will get access to one of two pairs of extra characters. Players will either get Michelle Chang and Angel or Kunimitsu and Ogre, depending on which retailer you buy from.
Normally one would assume that the characters would become available to everyone as paid DLC, but based on comments from Tekken creator Katsuhiro Harada, the characters may eventually be available for no extra charge. Then again, Harada isn't the president of Namco, so I wouldn't take his word as gospel on the issue.
As for the US version of the collector's edition, pre orders, etc, more information will be forthcoming, but don't expect too much to change between regions.