I have just enabled a feed for all comments on the site. Most importantly, this will include all replies to forum messages, so you can keep track of all the forums with a single feed. I’m not sure if it also contains initial forum posts, but if not, you can get them with this feed.
The forums have been pretty active, but I’ve been a bit concerned about them being hard to use. Hopefully this will help. Let me know if you have any comments on how the forums can be made more useful.