I have not been able to find an existing method for getting such notifications.
However, I've set up a repeating reminder in my calendar to check release statuses internally; going forward I will update these Targeted Release KBAs with the release date and make other announcements as appropriate until a truly automated process can be developed. Subscribing to the KBAs should then result in automatic notifications to you when new rollups are released.
cheers,
-bret