Ok so it turns out my ESP32-CAM has the gpio 12, 13, 15, and 14 available so this should map directly to the Jackpot expansion slot.
I got bidirectional communication (just UART @ 115200 baud) going with an Arduino pro micro.
That means I can start on the pendant without needing the rest of the board, and it should just drop in when the time comes.
But before I get too far, I should probably take a look at how it would integrate with FluidNC before I box myself into a corner in the API definition.