Per-group/node RSS feed aggregation?
I eventually wrote an entire module for this purpose. Basically, I have a 'feed' field for the group-type content type, and my module tracks that field and any changes through core hook_node_update, _delete, _insert, etc. hooks. Then I have a cron-based queue consumer that grabs the 5 feeds that were updated furthest in the past and checks for new content, then posts it into nodes under the feed's group.

I used SimplePie to help with the parsing, because even SimpleXML is somewhat of a pain. Anyways, I might try to make this functionality more formalized and port it to work with something like Organic Groups, but it's really purpose-built. If anyone would like some help doing something similar, give me a shout.