With the emerge --use-ebuild-visibility, binary packages are not rejected when the ebuild is masked or unavailable. I'll post a patch to fix the problem.
Patch posted for review: https://archives.gentoo.org/gentoo-portage-dev/message/32eaa7673026dd8a1f8aca01417ed173 https://github.com/gentoo/portage/pull/143
This is in the master branch: https://gitweb.gentoo.org/proj/portage.git/commit/?id=e309323f156528a8a79a1f755e1326e8880346b7
Fixed in 2.3.6.