As another interesting thing — there is also some work going on to post comments from the reader as well.

Besides, we actually can; neither you nor I promote the Blogger feed URL in our page auto detect settings; we both use a Feedburner improved version (and format changing) feed derived from the original, which has already underwent substantial modifications from the markup of the source content.

Nothing stops us from adding another layer of comment linkfeed markers atop that, either with help from the busily growing and self-improving Feedburner service's crew, or by ourselves, perhaps by making another Ning application that takes a post URL and creates a comment feed channel for it, while also piping a Feedburner feed through itself, layering said comment feed's URL atop appropriate link elements within the feed.

It's just technology; anybody that proclaims themselves king over the territory may rule as they see fit. Standardizing things as we go along makes it more useful and increases chances of landslide popularization, but if it's good technology and easy to use, adoption will pretty much grow by its own accord.

While the feed formats could easily be extended (it's been done before, and most popular feedreading APIs that I've seen support 'non-standard' fields), I felt that such a move might be a tad out of place. Using this (or perhaps, alternately, a <link> tag with the same rel attributes) the feedreader can still get the URL, without having to change the feed format (since we can't do that in Blogger or many other services anyway).

For a decent kludge until that has been standardized (unless it has already happened in RSS and/or ATOM — I have not confirmed whether that might be the case already), I think your extension to the link attribute is a decent start.