I anticipate that the MoCo will, in the future, remove the voltage gauge and replace with a note on the BOOM stating Voltage "Yes" like they do with the oil pressure now ("OK")....sorry, just a random thought reading this thread.
My '12 did the gauge dance but that was due to the poor voltage regulators (and recalled). Replaced the regulator through the recall and no more dancing. I was having other issues (lights fluctuating) besides the gauge. You didn't mention it but are you having other signs of voltage issues? Light intensity (fluctuate with RPM), radio giving issues, hard to start? All good signs (among others) of a poorly operating voltage regulator....
You also mention it's steady at the battery at idle or while sitting. Have you put that voltage meter on it and monitored it while riding? Just thinking out loud....again.