I've been playing with the Adafruit Motor Shield v2 for some upcoming projects. I wrote a simple Gcode interpreter. With this you can write commands on the serial line and the motors will respond correctly and in sync. It would be pretty easy from here to extend the system to work with up to 32 stepper motors.
The code is available at https://github.com/MarginallyClever/GcodeCNCDemo
https://www.youtube.com/watch?v=BBanpDUTklk