For anyone following along… I’m leaning towards the use of auto-watched categories, as I feel the ability to unwatch any given topic puts more fine grained controls into the hands of the user.
This idea:
https://meta.discourse.org/t/watching-a-category-perhaps-the-best-kind-of-mailing-list-mode/27507
Combined with links in the footer:
https://meta.discourse.org/t/is-there-a-way-to-unwatch-a-topic-with-a-link/27505/
would be really nice.
The links in the footer may have to be plugin material, as the last time I heard, at least @sam was not fond of putting lots of links in emails.