Anyway, how did you manage to receive webmentions and set up an enpoint? Are you passing it off to some dynamic scripting language to handle?
http://webmention.io, which is a standard web service running separately from the blog itself, receives webmentions for me (it's a hosted service, though you can also self-host).
A Jekyll plugin pulls them down on site build, which I run periodically on a schedule.
I'm just too lazy to bother.
This is gonna be the case no matter how the content is passed in the request (I.e. url vs form encoding).
It's dynamic content.
What is your proposed solution for supporting dynamic content on a static site that doesn't involve running some kind of service on the side?
I implemented my website's (see profile) comment system based on a tiny perl script that tails the logs from my webserver. It's completely separate and no internet user is connecting to it. Any URL, followed by the string "/@say/" like, "http://what.ever/something.html/@say/Neat something" is added to the comment page.
What you've done is made the webserver a blanket endpoint, where the "API" and the "database" are your web server log files.
Practically speaking, what you have is a CGI script with a non-standard interface to the server. It's still subject to any bugs in your perl script, since you're still processing input from an untrusted location.
It's certainly clever, though!
If it were URL parameters you'd have them in your webserver log, but you'd still need dynamic code parsing that log for anything more advanced than "have a record of the mention somewhere".
WordPress dominates the blogging world. Jekyll, Hugo, etc, are drops in the bucket by comparison. Winning that market over is absolutely required if Webmention is gonna gain any level of adoption.