Hyde/L'arc, Dir en Grey, The Blue Hearts, and Anna Tsuchiya all seem like shoo-ins. Pillows seems likely.
Cocco has some real rockers, but I'm not sure if she has the mainstream cachet to deliver. Her biggest singles were her wussy ballady ones, not her frightening metal. I vote for 眠れる森の王子様-春・夏・秋・冬. No YouTube video, sadly.
I just hope they go for real J-Rock and not anime OP/ED stuff. I am also totally fine with them going with poppier, more mainstream acts - if it rocks, it rocks.
You are not going to get Boris. Sorry. Just like I'm not going to get fra-foa. Make your peace now.
I'm trying to think of bands that have a chance of making it ... Youjeen is kind of unlikely, but an Aya song or two is possible as DLC.
Oh, given how whored out it is to music games already, Mika Nakajima x Hyde's GLAMOROUS SKY is practically a guarantee. Which, given how much it fucking ROCKS, is fine by me. I can full combo the drums in Oni Taiko no Tatsujin.
[youtube=425,350]xKaUwvjxXF0[/youtube]
VIDEO EDIT: Found a (live) video of Cocco singing Never Ending Journey. Def. the best song of her past two albums, and has a pretty rock-ass chorus.
[youtube=425,350]9DMwNMxAl1Q[/youtube]
VIDEO