I would consider it handy to have following feature in portage. /usr/portage/<type>/<app>/... path for ebuilds that come with rsync /root/.portage/<type>/<app>/... path for ebuilds that one has done himself and has not yet submitted or have not yet been approved to gentoo server. This would give standardised place for own gentoo .ebuild files that for reason or another are not (yet or at all) accepted to general use.
2.0.24+ addresses this with PORTDIR_OVERLAY support