EAPI=5 has it's own implementation for usex, but repoman will still complain about eutils.eclass not being inherited
This is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=7213586e1bdfbab66ddb21284eddbd9b51c28cb1
This is fixed in 2.1.11.39 and 2.2.0_alpha150.