We are currently testing a new module that will allow site visitors to subscribe to any RSS feed from any website. The module will go out periodically and check the feeds for new content, then send an email to the subscriber.

This will work especially good with the content publisher module. As a matter of fact it is designed to harvest the available feeds for that module.

I'm sure there will be some clean up required, but it won't be long before it is available on all installations.