Publishing as a patch for interested early adopters and risk takers only.
USE AT YOUR OWN RISK UNTIL OFFICIAL RELEASE IS SIGNED OFF ON.
Implements OnlyOffice Document Server 7.2.1. Confirmed in a limited way to work with Nextcloud 24 and 25. Upgrading the plugin appears to work correctly as well.
If you see a message telling you "The editor version has been updated. The page will be reloaded to apply the changes.", you must log out of Nextcloud, clear your browser cache, restart your browser, and log back in.
Screenshot of "update" message: 