Man, I want that!!! My CP is gonna be confoosing otherwise.
Of course, it would require a parseable list of all games and what panel controls they use.

Think that'd take a while, esp. if rom/game names change, and it has to support clones too.

Best way to bring the light to the panel buttons would be fiber optic cable. Then the big honkin' array of LEDs can be somewhere else, and you can use tiny ones or even prepackaged LED banks.
If I had any idea how to go about programming a custom windows applet to output to parallel port, I might try it.