FeedAPI and category domain parsing

I've been reading this post about an enhancement to feedapi and common syndication parser:

http://drupal.org/node/246938

What I'd like to be able to do is map categories, by domain to target taxonomy vocabularies using feedapi_mapper. So, any category with domain "Foo" could be mapped to taxonomy vocabulary "Foo" on the target system. Otherwise, you have no option but to dump all tags into a single vocabulary. Domain would allow intelligent mapping.