Apparently as of Mac OS Sierra 10.12, Time Machine can run over SMB. However there is some work that needs to happen to make this work, so not just any SMB share will appear. Apple has a specification page for Time Machine over SMB. I know LimeTech has wanted to drop AFP support, getting Time Machine running over SMB would surely drop my resistance to that!   https://developer.apple.com/library/content/releasenotes/NetworkingInternetWeb/Time_Machine_SMB_Spec/