You could say the thought had crossed my mind
Exp Module 1.PNG
Cool! So you'd place the female connector on the top side of that PCB? This adaptor and the Atari cart would stick out quite a bit, but it would be fun to have anyway. I can imagine playing paddle-based 2600 games like Circus Atari using your Spinner controller.
Also remember there is an expansion port with an additional 17-18 IO pins.
It's too bad Intellivision carts have 44 pins. Otherwise you could have had a three-console-in-one magic solution. (Could the controllers on the Intellivision Flashback be compatible with the D9 connector on the Phoenix?)