Looks similar to what Indieweb proposes for replies[0]: write a post on your site, than "ping" the original via a Webention[1] to let them know there's a reply,

Looks similar to what Indieweb proposes for replies[0]: write a post on your site, than "ping" the original via a Webention[1] to let them know there's a reply, rinse repeat. At that point anyone could build a service to unroll those conversations. [0] https://indieweb.org/reply https://indieweb.org/reply [1] https://indieweb.org/Webmention https://indieweb.org/Webmention