what if rss or atom had a way to say that a post was in reply to another post from another feed. and feed readers let you display posts in threaded order
what if atom had a way to embed a copy of the post you're sharing or replying to, not just link to it? i would say just add a second <content>, but that’s forbidden :(
edit: hmm how about nesting <entry>, or putting an <entry> inside the <link> (instead of self-closing <link/>). per § 6.4.2, we may be able to nest <entry> as long as we have a foreign element in between, like <atom:entry><cohost:reply><atom:entry>