If I understand correctly the Ethernet smooth stepper will not do rigid tapping ? Is it possibly a future function that will be added ?

Andy at Warp9 has said that rigid tapping is something that they are interested in doing but it will be a while before they complete it because there are higher priority requests currently being dealt with.
Your guess as to when is as good as mine 

Tweakie.

Hi,
can you run your spindle as a C-axis, that is to say do you have position control of the spindle?

If so you can do rigid tapping and it does not require any special features of the controller.

Craig