Another interesting piece that's related to webmention and feed readers is the <a href="https://www.w3.org/TR/micropub/">W3C Micropub spec</a> that I believe was released on the same day as ActivityPub. There are already feed readers like www.woodwind.xyz that allow you to not only subscribe and read your friends who publish to their own sites, but you can use it to micropub "likes" and "replies" to those posts directly from the reader and to publish them directly to your own website if it supports the micropub spec (and yes, there's already a WordPress plugin for that). These micropubbed posts can then, in turn, send webmentions from your own site to your friends' posts to be displayed as comments there.
More details on all of these and how they can interact can be found on the wiki at https:/