The RSS Advisory Board is currently discussing a formal RSS Feed Autodiscovery spec. Leave additional feedback in the comments here (only board members can post to the mailing list).
Randy, I'm glad to see the recommendation of choosing a single feed format, but I'm not sure about recommending choosing a single feed. I really like it when sites that offer more than one feed (ex: main feed, comments) provide auto-discovery of both, provided that they use descriptive titles for each. When multiple feeds are offered, it would be nice if the auto-discovery link had a way to let user agents know which is the primary feed.
I suggest warning people about including multiple links to the same feed (presumably different feed versions) because aggregators can't differentiate them from links to multiple, different feeds. They therefore have to reports all links as separate feeds. They can suppress a feed if the reader is already subscribed, but they get no choice about reporting all other feeds.
As a result, multiple links to the same feed will result in aggregators suggesting readers add feeds they already have.
Unless, of course, there's a good way around this issue in which case the spec should explain it.
Hope that's of use,
Sorry, just re-read and I see you have suggested more restriction that I envisaged. Might be better to explain the issue in a bit more detail to better inform feed creators.