I'm not clear what a minimalist machine should have for features. It could be any old working sewing machine one could find. The needle position control would need to be adapted for whatever model one uses. Is it practical to provide a "universal" design that fits any used sewing machine?
I didn't finish dabbling with my homemade motor controller and encoder for the needle position detection stuff. So more fundamental work would be required to make my Kenmore_6 work.