The Atom standard tried to support commenting directly in the content feed. There was a threading extension to incorporate comments in the feed file itself and a publishing protocol so that you can post a comment in standard way from, say, an app.

If that caught on with podcast apps and publishing backends there would be no need for a centralized system. Unfortunately, the adoption of that was practically zero. To quote the Indieweb wiki [1]:

> readers supporting atom comments: (?)

[1] https://indieweb.org/Atom