[simonair]

Thanks for your investigation. Regarding the proprietary mode Apple claims to be required, I guess this mode allows an AirDrop link to be established without disassociating from the (infrastructure mode) WiFi base station by switching between the two links quickly enough. Obviously Ethernet has no such limitation. Indeed, in my opinion, AirDrop is more useful over Ethernet than WiFi.

[gonzo]

Multi-mode WiFi drivers became the norm less than 10 years ago. The trick here may be getting all the devices involved in a given AirDrop session on the same channel.