I can see some impediments to a system that relies on technology for pitch calling. System reliability- how many times do we hear about the comms going out between the QB and the sideline? It seems almost weekly. There are built in redundancies in football as there would be in baseball, but what would be the costs of moving to a new system in baseball i.e. longer games, delays when the comms get wonky. Also, the catcher only has one free hand to free to use a signaling device. He certainly can't speak what the pitch should be with the batter right there. So he'd have to use his throwing hand to signal to hold and use a device, then store that device all while setting up for the pitch. Seems clunky. Especially when you factor in that the pitcher and catcher aren't always 100% on the same page and shake offs happen.
How would the pitcher receive the signal if it's not auditory? Maybe a haptic device that vibrates once for a fastball, twice for a curveball? What happens when a team develops an algorithm that uses a camera trained on the pitcher's feedback device that can tell how many pulses are being signaled?
I think you could make the argument that hand signaling is a technology, and the beauty is in its simplicity. There's a built in layer of obfuscation which should keep the other team guessing, so I believe it's a quite reliable system. Of course when teams start using more advanced technology to steal signs then maybe the old system needs to get updated.
It's an interesting idea, though. I'm sure some smart folks could put together a system that works.