Looks like a bigger version of something I built. In my case I built it as a progressive enhancement to `<time>` itself (like `<time is="relative-time">`), which also potentially makes it easier for it to gain features if the tag gains features. Of course, the most obvious (and disappointing) trade off to that approach is lack of Safari support [1].
[1] https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...