Webmentions came up with our current Trackback/Pingback discussion. I wanted to raise it here as well. See https://indieweb.org/Webmention, there now is a W3C recommendation and we could think about implementing it.
That is, someone else could think about it (Garvin, are you interested?), because I made up my mind that I hate this spec. It is just trackbacks, made incompatible. If what I got told is right they started with Pingbacks, and from the looks of it then re-implemented trackbacks without knowing that standard. So now we have three, grr. And it would have been so easy to just add a proper discovery mechanism to the trackback spec and to combine it with their new presentation suggestion.
A way to implement it anyway could be https://webmention.io/. The website does not present it, but the developer told me they have a feature where you give them the webmention you received and you get send back a pingback to your site. The website only presents the other way around, and focuses on getting a notification via JS and Websockets (wtf); maybe they scrapped that, but something to investigate. I also let open an issue to do the same for trackbacks, as it would be laughably easy, but there was no further feedback and nothing seems to have happened.
I think it would be saner to focus on improving the trackback discovery mechanism and add in a round of testing making pingbacks work more reliably, there are some corner cases where it does not work well, and some spamblock settings (like the IP mismatch of sender and receiver) that kill it for modern server setups, meaning we should warn against activating them or just remove that option. We could also focus on getting things like the tweetback mechanism to work again. As far as I know Twitter removed all means for that, but I think Facebook still supports that (the counter in the shariff plugin might be a good indication for where something like that is possible), and maybe there is a standard for plattforms like gnu social – I hope it is not webmentions.