How do we purchase the upgrade kit so we can upgrade older mk3's with the old driver chips to the new boards with the new driver chips?

Has anyone tried replacing the switch (and possibly all of the electronics) so the motors are controlled by either custom electronics or directly by a printer's GPIO lines? I haven't ordered a 3D chameleon yet, and I haven't found the schematics. However, I'm considering getting the 3D Chameleon, removing the switch and electronics, connecting a custom microcontroller to my printer's GPIO lines, and then driving the motors from my microcontroller. Has anyone already tried this?