I can’t help but think that 8 bits is all we need to send data for any motion control that we might need for a 3D printer. 6 bits for step/dir, 1 bit to select between two sets of stepper motors to control and 1 bit to select an alternative use for the other 7 bits. If just 1 set of motors then there are 2 bits to select different modes. An i2c or spi module that does motion control could be added onto a cheaper board with not enough controls easily. That could make an add on set of 3 stepper controls as cheap as $12 or an add on set of 6 stepper controls as cheap as about $20. I am just making a guess on the prices based on component costs and some finished product costs. What do you folk think?