How about a small handlebar mounted FRS transceiver or even a CB transceiver with built-in (SR10) BT capability designed specifically for motorcycles (waterproof). With the CB frequencies, the antenna would be longer so remote antenna mounting would need to be considered. But with the FRS frequencies, the antenna could be built into the unit. On a standard transceiver, the display and battery compartment is a large part of the size. So, eliminate both to cut the size way down. No major external controls. Mainly controlled by the helmet headset. If Sena could design one with the CB freqs, they just connected to a large section of H-D, and Goldwing riders.
Transceiver with BT built-in