DRAFT - not finished
Use bluetooth instead of FTDI - it might be easier:
Seems to do what I want: https://hacks.mozilla.org/2017/02/headless-raspberry-pi-configuration-over-bluetooth/
https://www.cnet.com/how-to/how-to-setup-bluetooth-on-a-raspberry-pi-3/
$ bluetoothctl
# agent on
# scan on
wait a few minutes. grab MacBook MAC Address
[NEW] Device A8:86:DD:96:E1:4F MacBook Pro
# connect A8:86:DD:96:E1:4F
# list
Controller B8:27:EB:9D:C9:0D jeffs-radio [default]