Impressive work so far.
Would be nice to have a pin header of contacts closures on the PI board. Combined with some programming options, specific contacts could trigger specific video clips...
Simply connect those contact closures to specific insert light sockets (like the typical mods do), and wow, what a cool interactive mod that would enhances game play even more!
For some titles, like Indiana Jones (Treasures) and Scared Stiff (Skull Pile), you could even take advantage of the built-in wiring harnesses that were unused on production games due to cost-saving measures at production time.