Soldered up the board with caution, but it appears that the whole thing works fine. Currently I’m testing at 12v and the only problem I’ve noticed is that the new ATX power supply I’m using does a poor job of handling large current spikes. Tests have gone very well, no signs of back EMF or noise bleeding into the IO board or causing oddities.
Next I’ll be wiring it up for 24/50v testing and, assuming nothing goes hilariously wrong, it’ll be time to start seriously looking at the graphics and software. The hardware is basically feature complete beyond replacing a few temporary off the shelf parts and building some wiring harnesses. I still might need to do another run of the IO board to solve the cabinet switch issues, but I’m still hoping I can get away with some creative wiring.