And OpenDesk has managed to do without, they seem to be using Univention Nubus as an AD Replacement

https://www.univention.de/loesungen/alternative-zu-microsoft...

Is there a combination of open standards to drop in to replace AD integration with self management?

OAuth enabled systems aren’t enough, central management of users and machines are huge. If that core matures, it opens up the market for replacements in other areas. Teams, Outlook and the Office Suite need first grade replacements.