Actually, I'd like to build a small 3D CNC milling machine, but I want to use as little number of pins as possible, so if I multiplex the common pin on all three motors, I can use 7 pins on my MCU instead of 12. Also I only need 7 MOSFETs to drive all the steppers.
But then, I can only use one motor at once and I lose a bit of accuracy.
Or should I use two serial to parallel 74HC595 latch shift registers? It'll be more of a pain in the ass but I'd maintain all control. I'd need 12 MOSFETs, but only 4 MCU pins.