All it needs is 2 control ports, so you can plug in any 2 of: control set, HiFi module, Bluetooth module. Or offer an external "hub" that turns the one control port into multiple. Or have a pass-through port on the bluetooth module. Probably the most important is to be able to run the BT module alongside one of the others, so you have a backup in case the phone app crashes, BT connection drops, phone battery dies or you're on the phone when you're shot and need to JTK somehow. An external switcher works but it's a bit kludgy.