STAS and Samba AD server

Has there been any consideration for an alternative AD server. Currently I am using a SAMBA 4 AD server for my single point of authentication for Windows, Linux, and OS X. It would be really nice for the SMB sizes that can not afford a Window Server license that are utilizing this type of solution to be able to integrate STAS to decrease the overhead of managing users and being able to track there users without having to give everyone static IP addresses.

Looking forward to see where this goes.

-Ron