@bouncepaw @KevinMarks just to clarify "I used to...", I know I implemented it, I'm pretty sure my Flutterby(dot)com CMS will happily accept WebMentions, and I may even send them, though that might be a manual button, but I don't think I ever found one in the wild.

And I had all of the same spam concerns over doing the same behavior with "Referer:" headers and TrackBacks and PingBacks and whatnot, if it ever took off.