Advanced features like copy, scan, maintenance, etc are not supported at the USB port on any of the Apple routers, as far as I know.
Unfortunately, Apple can only use the drivers that are furnished to them by the printer manufacturers.
I know of no manufacturers who have developed full function drivers for use at the Network USB port location. Most manufacturers do have full support for a wireless connection and also Ethernet to an All-in-One device.
The moral of the story here.....if you want your All-in-One to function on a network, you need to make sure to get a network All-in-One device, not a USB device.