As an extra note: If they really add extra characters through DLC, they have quite a few that would need to be added first and/or would sell better than a new one; namely, Kotori, Eri, Ai, Yumeko, Cineria, and maybe Ryo. Sure, the game wasn't as good as the others, but their inclusion in the anime, to a degree, shows that the characters(at least, the main ones of the game) haven't been forgotten.
Also, I'd really want to see the Maou Angel girls as DLC, even if as a rival group a la Project Jupiter, with only one or two songs. Just having Tomomi in the idolmaster 2 graphics would be worth it, no matter the price.