I think it is a matter of preference for each customer. All 5 of my machines run under Windows. It's what I know and is cheap and easy to replace upon a failure. In fact I have two stand by laptops ready to take over a machine when one fails or faults. 3 of them use IBM R40 laptops with XP.
The new Pulsar is different in that it has an on board computer with an SSD and Win7. Fast boots. It also has Smooth Stepper Ethernet. That makes it very stable. I have not had it lock up like some have in the past using a PP. Still waiting on a new Arduino BOB. It has a proprietary BOB now, but the Arduino should prove nicer and even more stable. This is the direction I would probably go.
Now it does have a Servo spindle and I gotta tell you, once you go rigid tapping, you won't look back. For that reason alone, I would probably source some of my electronics from Novakon.
I like and have plenty of tooling for R8. That is already an investment.
I would not invest in something else. R8 does fine in even a little larger machine, so it is fine for one this small.
Like Defeng, I think you should design possibly two heads or offer two spindle cartridges. R8 being one of them. You are trying to bridge the gap between hobby and pro. That would help.