After what I went through on the BMW, this is what I would try.
See if you can find a BMW EWS sensor ring. THey ended up being pretty cheap because they sold a ton of them, and people were pissed off. The part number has to end in 247. If you post locally, I bet GS riders have spares to loan you.
Adapt the wires to this new ring, use your spare key inside it to communicate to the ECU that it is the right key. Turn your key switch on with the other key, and see what happens.
RFID key Identification has been around a long time. Just not on bikes.
Also I would trace the wiring from the antenna ring to the ECU and make sure it was not pinched or damaged by the factory. Shouldn't be too hard if the tanks are off.