Pressure sensitive flipper buttons. The harder you press, the harder your flipper fires. Of course the shots would be designed so that different hardness is required to make different shots. There could be a pressure sensitive target too that adjusts throughout the game sometimes requiring a light shot to trigger the switch and sometimes requiring a hard shot to trigger.
How about a target on the playfield that says ‘nut shot’. Every time you hit it, a boxing glove fires from the coin door. Even better if we can get some kinda optical sensor with AI that makes up for the cheaters that are trying to dodge it. I’m not sure what we do for the ladies on this one. Maybe it’s not a great idea after all.
I could go on, but the rapid decline only accelerates from here. I dunno: maybe tank treads? Maybe Mick Jagger dances around on a post? Ooh, I know, a playfield that self deteriorates within the first hundred plays…this could create some great aftermarket revenue! … … nah, I still like the ‘nut shot’ better.