I am not too enthused about spamming users on the site with notifications or topics automatically. On meta-only, maybe…
But I think it may make sense to have “digest emails” have a section that teaches users about recent changes.
Here is the new content you missed out on!
Here are some new recent Discourse features you are not aware of!
We would have to be very careful here, but making a more powerful digest is always a good thing. It also ties in to allowing admins to occasionally add content to digests which can be very powerful.