If an enhancement is filed for new ebuild inclusion, and someone wants the ebuild, there's no search criteria by which users can filter the bugs in which an ebuild is really required.
For this I suggest a new field 'ebuild required', with 2 values yes/no.
It'll be a better idea to make a link in bugs.gentoo.org's index page to point to such bugs.
You can do a search for bugs in the Ebuilds component not having the EBUILD keyword.
Sadly, this keyword is not used consistently, and I doubt a new flag or keyword or field would fare any better here.