to prevent mistakes in encoding, we should reject ebuilds that do not decode as utf8. i think we already do this for metadata.xml, but we should expand it. i would also like to see it apply to patches, but since we have to patch upstream files that not might be utf8 encoded, we can't enforce it there easily :(.
in fact, PMS already requires ebuilds be UTF8 encoded :) Ebuild File Format ... The file encoding must be UTF-8 with Unix-style newlines. ...
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.
pkgcheck has InvalidUTF8. Not sure if it's sufficient.