The technology in the slot machines by WMS and Bally are pretty amazing. Some screen illusions are really convincing. Its a shame that they're no longer in the business of pinball.

Any cell phone app integration. Connect the pinball machines to wifi or bluetooth and create an interface so that people can interact with the game from their phone. Maybe an achievement system, or a way to "save" your progress on the game to encourage repeat plays. Heck, maybe even integrate apple pay or android pay so that coinage doesn't have to be an issue.

Also, connecting the pinball machines to wifi could give them the capability of automatically alerting the operator via automatically generated email or text message that certain functions of the game need servicing (broken switch(es), solenoids, bookkeeping alerts, etc). I'm really surprised that hasn't made it's way into the software and hardware yet.