This limitation exists in NS7 as well. The multi-DC scenario is still unavailable in NS8 because Samba lacks a built-in Sysvol replication solution. However, it should be possible to provision LAN-accessible DCs from the CLI. I believe this works at the DC level, but I’ll verify limitations regarding UI compatibility. Note that Sysvol replication would require an external tool (e.g., a Windows-based scheduled xcopy between Sysvols).
For a file server-only solution in NS8, a dedicated module with the Samba Domain Member role is an obvious choice. Container images already exist, and they could be the base for a Nethforge project!
Beside that, I’ve had encouraging results experimenting with the RODC role.
The main advantage of the RODC role is that it does not require a machine account like a Domain Member. It involves minimal configuration, provides shares like the DC role, and can be implemented using the existing Samba module in NS8 with a special procedure.
We used the ldapsam:// database in NS6. Since Samba 4 introduced AD support, there is no need to revert to ldapsam for file server setups.
TL;DR
Both multi-DCs in a LAN and RODC file servers can be achieved with the core Samba module. I’ll confirm the feasibility and, if successful, provide a how-to guide.