Would you consider adding "Grouping" to the metadata that Rip will accept, Stephen?
It's not something I've used in the past, but I've noticed it recently in iTunes - don't know how long it's been there. Apple seems to use it as a standard field: it comes up by default in one of their new views, and they populate that field on some iTunes Store downloads.
I guess it could be useful for sorting some types of music within iTunes.