I’d love to have a crack at this if you haven’t started yet @zogstrip 
UPDATE: Ah, right. There are RSS feeds for latest topics and topics within a category, but the rss format doesn’t quite lend itself to top topics because the order of the feed can change over time (i.e. posts can swell or drop in popularity, which won’t be reflected in the feed short of them being published twice.)
One possible solution could be to publish a periodic [weekly? daily? Controllable by site setting?] rss feed of top topics, which would be an aggregate of the most popular topics for that day/week. I’d be happy to work on something like this, but would probably need a little support spec’ing it out a little.