That's a cool idea, thanks for the diagrams. Also uses less pins.
So TX is not needed for downloading a sketch? When I download a sketch, I seem to see both TX & RX lights on the FTDI board flashing, so I figured TX is needed, too.
I'd still like to talk to each unit when I need to. Perhaps I can implement a "unit select" pin, so the controller has 2 specific pins for each unit, one to reset a unit, one to 'select' it. Also I can use port extenders easily for this process, so I could control plenty of units from each controller.