Has anyone ever considered building an email extension of the Webmention specification?

By that I mean, a sender attempts to send a mention and if there is no endpoint or the send fails, then as a back up, the sender parses the receiving site’s page for an h-card and if an email address exists, sends an email notification there instead?

Might be helpful for those who don’t yet have Webmention set up, but could act as a backup. Then when they have things working later, they could force manual mentions to recollect them? Also useful for those who’d like notifications, but don’t want to build infrastructure or who might not want to show comments on their site either.