I'm happy with a minimal approach to the automated strike zone. I think having a fully automated zone is going to take too much away from the game. I actually hate the idea of it. There is so much art to pitch framing and a pitcher using an umps zone, when he's consistent, to his advantage. I do think having the challenges available for when they miss is a good idea, but let's keep the umps calling balls and strikes. Also, could challenges only be successful if they are clearly outside of the zone vs missing by a millimeter? Part of the entertainment of baseball is the back and forth with the umps and the fans reactions to what they think are bad calls. It feels like we will lose a lot. The game will feel uneventful on all called pitches.
My one concern with the challenges will be the coaches getting instant feedback to batters with some sort of signal or noise. That could be tough to monitor.
I think it will be funny when you get some goofy guy like a Manny Ramirez, who won't listen to his manager and will wildly use challenges and burn them up in the first inning. I don't know of Manny is the right example but was looking for a guy who is in his own world.