@Zach_Kaplan (just in case you are considering selling the controller board)
I would envision two scenarios here.
One. ----- Someone has a problem with their controller board (16039) and they need to buy a replacement (a driver chip goes bad or some such thing). This would just be a bare controller board that they could swap out with the defective board in the X-controller.
Two ---- An electronics upgrade kit. It would consist of the controller board (16039) with the heat sink mounted, the plug in connector modules (4) for the stepper motor connections, a 3-pin pigtail for the power connector, and two IDC pigtails for the logic wires. Such a kit would slide right in to replace the Arduino/gShield electronics (you would need to supply your own case).