Thanks, that looks very useful! I wrote a script to export Markdown from Joplin notes (https://gitlab.com/stavros/notes/), but the UI in this site is better.
It’s custom.
If you got time and energy in the near future, please, consider slightly enhancing it according to the average web surfers expectations. Particular irritants were the broken scrolling (bound to a container), the broken footnote links and the forbidden content behind links. Additionally the classic escape hatch, Safari Reader, didn’t work.
Sorry. I built it in a weekend several years ago and haven't touched it since. Someday I'll give it some more attention…