My wish is that everybody wakes up one day and figures out that light up buttons on arcade machines look like crap. It makes the cab look like a redemption machine.
I'm not a fan of illuminated buttons, but do like the idea of button labels (on the CP) that change on the fly to match the game.
It would be great to launch a random sports game in MAME and know what all the buttons do without using trial and error.
I did some tinkering with printed labels underneath dark plexi, each of which could be illuminated by a single LED.
Being limited to already printed words, I never came up with a layout that accomplished what I wanted.
Small OLEDs would be cool. It would be hard to squeeze SHOOT/BLOCK onto one of those matrix displays.