ongoing • On Comments (II): "Antone Roundy, and others, point out the problems with per-entry comment feeds; namely, that various idiotic clients will poll each and every one regularly from now until the heat-death of the universe and there’s no way to stop them; given the volume at which I post, this would be untenable."
We’re starting to get into this with Blogger. The comment feeds are all there in the new in-beta version — both per-post and per-blog — but there’s no Atom-to-Atom linking going on.
Probably the best solution is one where the feed reader would fetch the per-blog feed, which it could do regularly, and then filter to show only the comments for posts that the user is interested in.
Tim pointed to the Atom Threading Extensions, which I’m planning to investigate.