I bet they'd save "new" DLC (Overmaster, and what I hope will eventually be catalogs for Kimi wa Melody and Mata Ne) for after the PS3 game comes out.
Like, they don't want to release anything huge for the Xbox because they don't want to decrease their potential sales for the PS3 version (anyone who is going to get the PS3 version isn't going to continue buying DLC for the 360 version and vice versa, right?), but after the game is out they can release big, shiny catalogs for both consoles at once and not affect the other console.
So maybe next catalog will be another repeat/"old" song and costume, and then when the PS3 game comes out (should be before catalog 9), we'll be seeing things we've been waiting for Overmaster, along with new costumes again.