Not relying on preservation of xatrs would be a gentoo.git tree policy. If such policy is created, new QA check file would belong in gentoo.git repository in metadata/install-qa-check.d directory, not in Portage repository. (And there is no need to delete any xattr-related code in Portage in future.)
Creation of such policy would need discussion on gentoo-dev mailing list and/or formal vote in QA team.
