Been quiet so I'll throw in this topic now.
I'd like to suggest a feature that could make a big difference in playability for some folks: Lag compensation. Many modern monitors and TVs lag a few frames in displaying the input signal. And of course pinball games are very sensitive to precise timing. Last week trying to play Fantastic Journey, I couldn't hit any shots using my current LCD monitor because of the lag. It was fine after switching back to my old CRT.
Could the Pro Pinball program architecture support this for the Ultra editions? Basically it would need to keep a few frames of game state, and back up and re-simulate those frames whenever the input state changes. Guitar Hero and Rock Band are the most well known games with display lag compensation, as an example.