Hi Henk,
I'm not sure G70-74 relate to rigid tapping. But rigid tapping is supported via a Macro in Mach3.
see:
http://dynomotion.com/Help/Mach3Plugin/Mach3RigidTapping.htm
The same method should work with KMotionCNC. The only issue is passing down 6 parameters to the C Program to define the cycle. We recently added the capability for C programs to read Interpreter Variables so that is no longer a problem. If you would like to do this and can't figure it out I can help you.
I suppose the place for a wish list would be here on the Yahoo Group.
Regards
TK