Would it make more sense for email digests to be broken out as a plugin?
Forum communities vary so widely on their email newsletter preferences, and breaking it out of core makes life easy for those who don’t want to offer digests, plus it actually gives more flexibility for those who do want digests.
For example, on one of my forums, I run a daily digest opt-in, a weekly digest opt-out to active users, and a monthly digest opt-out to inactive users. Each of those digests is a different plugin from a third-party developer, so I can customize each one without affecting the others.
I haven’t looked at the code, but I suspect it’s trivial to break it out of core–I mean it’s really just a cron job plus a few SQL queries and an email template. Perhaps the weekly digest is a default installed plugin? A “batteries included” part of Discourse that can be easily swapped out if the admin prefers a different newsletter plugin?
Right now, with this integrated into core, I’d be a little hesitant to hack too much on customizing it to my site because every modification makes upgrades a little more painful.
Just a thought…