Actually Librehosters forked the https://github.com/fuerst/embed-etherpad-lite to support CodiMD (the “community fork” of HackMD) – which is being renamed again…
It’s very simple to use and you can fork librehosters / embed-codimd · GitLab for your own setup. It would be useful to have a setting for the pad host instead, but it’s more work. Librehosters use SAML SSO between CodiMD and Discourse, so only members can edit the pads.