The control software shouldn't even discussed, it should be left to the end user to decide what electronics and control he wants to use to run his machine. Too many options available, I might prefer Linuxcnc and servos to your steppers and Mach 4, kflop, edging cnc, etc, etc. Just build a good base machine and let people accessories on their own with maybe belt drive or direct drive mount option for servos or steppers.