Never thought about this before but once you have robo-umps you can do all sorts of things. You know how in bowling they will have this thing where the front pin is red every so many times and if you bowl a strike with the red pin you win a free game or snack from the snack bar? They could have a hologram of a small area show up in the middle of the strike zone and if the pitcher can hit it and the batter doesn't put it in play it could count for two outs. Or maybe everyone in the stands gets a hot dog.
The possibilities are endless. They could find ways to bring fans back to the game!