This idea was inspired by ulm in https://bugs.gentoo.org/687018#c2 "So the ebuild will need RESTRICT="mirror bindist". (Basically, every license in @EULA requires that, because we cannot ask mirror admins to accept anything.)" Reproducible: Always
It would be more complicated... Conditionals should be preserved. LICENSE="x a? ( !b? ( EULA_license ) )" would require RESTRICT="a? ( !b? ( bindist mirror ) )". LICENSE="|| ( EULA_license GPL-3 )" should not require any RESTRICT.
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.
I believe pkgcheck does this right now (MissingLicenseRestricts).