Occasionally people clean up last ebuild from package directory and don't realize that. Recent examples: https://bugs.gentoo.org/show_bug.cgi?id=621788 https://bugs.gentoo.org/show_bug.cgi?id=621790 I suggest adding an error to prevent that from happening by accident. Given that there is no existing 0-ebuild packages (except above ones) perhaps it's ok.
I suggest to make this a warning but not a fatal error, given that it is allowed by PMS: https://projects.gentoo.org/pms/6/pms.html#x1-360004.3 "A package directory contains the following: * Zero or more ebuilds. [...]"
Warning also sounds good.
repoman support has been removed per bug 835013. Please file a new bug (or, I suppose, reopen this one) if you feel this check is still applicable to pkgcheck and doesn't already exist.