"gentoo" makes a lot of sense to me. "gentoo-main" works, as well.
Anything with "ebuilds" doesn't make as much as sense to me, since it also contains profiles, eclasses, etc. In that vain, "gentoo-base" could also work? I don't really get the need for this whole namespacing thing, so I'd prefer to do without that. Cheers, Dirkjan
