I've been looking around for an answer to this but is there a way to change the audio so its a Vocaloids proper voice in the song? I've seen examples of it in say Len singing Just Be Friends which is usually sung by Luka and he has his proper voice.
Not that I doubt you but does that mean that http://www.youtube.com/watch?v=tNfbh1JSs1k, is just a really good video edit?
Yes. You'll be believing me when you have a game. (In other words, Inochi No Uta and Kouya to Mori to Mahou no Uta are the only ones that have sung in OTHER voices (Miku/Rin/Len).
To create a track for every vocaloid for every song is doable. All they need to do is replace the voice in the VSQ and maybe do a few tweaks and then remix. But I think the UMD's are running out of space. They wouldn't be able to cram all those extra tracks into just one UMD. But hey, I wouldn't mind an expansion pack or DLC with something like that. Actually I'm surprised they haven't done it already considering how easy it is.
that's the reason why the visual galery in Extend is so small. there are too much moduls and songs on the UMD and THREE videos instead of one in the visual galery so there wasn't enough space for more illustrations.