I think that you are spot on - your suggestion would bring a big dollop of sense a bit of the user preferences that have always caused me and my forum users confusion. You capture the four main options that people want:
- Heaps of emails
- Some emails
- Just the Activity Summaries
- Nothing
At present, users have to make it up from a few different places and some unfamiliar concepts. So most don’t bother and just stick with the site defaults (unless they get there via the email unsubscribe thing).
I’d nest Emails under Notifications in the /preferences as well.
In Mailing list mode, are all notifications suppressed at present? Because that would be super useful. I’ve had several users complain that when they visit the site (infrequently) they are overwhelmed by the number of notifications for posts that they have already read via email.