http://www.intertwingly.net/wiki/pie/DifferentlyAbledClients
Sam,
Actually, I was thinking of the pre-Atom piece you wrote:
http://www.intertwingly.net/stories/2003/01/26/evolve.html
If Atom were to ditch the reliance on HTTP purity and stick to passing around chunks of markup, then I could implement Atom with a few trivial code modifications. I could literally change a few variable names and be done, and it would arguably be more efficient without the XML-RPC library as a middleman.
But if I'm going to end up having to implement a pointless digest authentication system (I'll believe that's important when Blogger ceases to have an HTML login form), fiddle with HTTP response codes, and generally rewrite the whole thing... well, the exercise rapidly loses its charm.