It seems to me that all the best mods have enable the games to be played in the manner intended. Monitor rotation, auto joystick selection via a 360 or a servo, all the amazing emus out there to help recreate the way it was in the arcade. Part of that nostalgia for cocktails was that people had to take turns. I do really like the split screen hack that is already out there, but there is something about playing a screen flipping turn taking cocktail game. For that reason I just don't see juice being worth the squeeze. Doesn't mean it isn't a valid mod but it isn't something that I would want to take the time to integrate.
I would really like to have a room where the floor and walls were lined with RGB LEDs and the ceiling had a kennect type tracking device so I could be Pac-man, that'd be cool, but that doesn't have anything to do with retro gaming. Not everything has to but if you want an off the wall feature then I recommend you start making it yourself. Now if you'll excuse me I have to go hotglue 7.3 million LEDs to my garage floor.