see where you're coming from. Japanese RPG's won't be too big for DVD9's (the actual game data), but if they want to fit hours of HD video on there BRD's are the only way unless you want 5-6 disc games.
Well I don't think they need 5-6 game discs . 5-6 dvds would be a good 8 hours of cgi or more at 720p
I could see them using 1 or 2 discs for cgi .
It should be just fine . You don't take into account the reuse of textures . Textures are used many many times over and over again and they will be compressed using the native compresions of xbox 360 . They will have the dxtc formats , they will have 3Dc and I believe ms siad something like 30 diffrent compresions in it . These textures will be compressed onto the disc and since its a fixed platform you only need that compressed texture . Unlike a game like eq2 (which i believe is around 4-5 gigs on a hardrive ) where you have diffrent target reses and diffren't video cards . Thus you repeat many textures .but what if a dev wants to make a GTA-like title that's 2-3 times the size of GTA:SA (that would be mucho expensive to make to be sure)?
In all honesty its hard to make a case where bluray is more important than hdd . Now if you rather watch movies than games bluray will be better , but I don't think thats truely the case for gamers