OK, 4-5 years ago I was hired by a startup building a data storage/sharing hardware solution that emphasized security. Each storage device could be a an ad hoc member of a group of devices and there were multiple users for each device/group. Individual chunks of data (be it files, filesystems, dirs, etc) had ownership and privileges as did the devices themselves.

What the startup did NOT want to be is the single source of authority or federation for permissions, group membership, user management, etc (they would not only become the single point of attack but the devices themselves would be dependent upon the existence of the company continuing to provide federation services, so going-out-of-business would render the devices useless).

The most obvious solution to those issues was a blockchain-based system. As long as devices existed they could continue to interop, the entries in the blockchain provided audit trails, the entries could be replayed for sync purposes, etc.