I've thought of doing something similar, but exposing it as a USB-Ethernet adapter instead. The Pi 4 (and Pi Zero W) support USB OTG. It looks simple enough wit

I've thought of doing something similar, but exposing it as a USB-Ethernet adapter instead. The Pi 4 (and Pi Zero W) support USB OTG. It looks simple enough with a single command with Linux USB gadget to create the network interface usb0. Then you can do power and data over the single USB port.