I propose adding the rss capability to the group feeds. So Discourse Meta would give you the rss feed for all trust_level_0 users for example.
Use Case #1: We have slack notifications that are pulling the rss feed for new topics. I would rather have a feed of all posts, not just new topics. Looks like the groups already does this. So to get a feed of all activity I should be able to do: Discourse Meta
Note: The one catch to Use Case #1, is that the everyone group, unlike the other automatic groups, does not appear to offer a group feed.