Actually, Namco Bandai had a Dragon Ball Butouden series in the past. Three Dragon Ball Z: Super Butouden title were released for the Super Famicom. The last Dragon Ball game to bear a Butouden subtitle was Dragon Ball Z: Shin Butouden for the Sega Saturn.
Namco Bandai also registered Zenkai Battle Royale. Since "Zenkai" is a Saiyan-only power we’re guessing that’s going to be for another Dragon Ball game.
So, what system(s) do you think Dragon Ball: Zenkai Battle Royale and Dragon Ball Z: Ultimate Butouden will be on? I recall Namco Bandai had a Dragon Ball game in their tentative 3DS line up. *checks* Yup, they do.