> But you are correct that a built-in Ethernet device will be preferred most often if it's available.
Actually, my concern was just the opposite: that the built-in Ethernet or WiFi adapter might _not_ be preferred over the USB connection, which can only access this one device. Link-local access to the device will probably work just fine, but if the system selects that adapter as the default route there will be unfortunate side effects for the user's LAN/Internet connection.
> Of course since nobody does this today it probably wouldn't actually work right out of the box if you tried it.
That was my point. Sure, all the pieces are there, but the reason for making it an RNDIS interface to begin with was to avoid the need for any extra software. If you have to reconfigure the system or add special support for such devices, you might as well just include the more secure filesharing-only USB-to-IP proxy I originally suggested.