I agree this may be a nice additional option to the errata notification. In 6.5 you could achieve similar report though through report engine. There's a report "Applicable errata" that can give you same results and supports hosts filtering. It can be triggered through API from cron and the result can be send via mail. In next version we'll have mailing support for report results built-in. Does this solve the use case? If not, what is missing.
After confirmation, this can be considered resolved by report template "Applicable errata" in 6.5, closing as current release