Similar to the "hole drilled through the kitchen table" problem of the HomeView ad, seeing the hands/arms floating in to touch the screen immediately makes me imagine the impossible ergonomics of reaching across a keyboard to touch a screen.
Steve would agree: "We've done tons of user tests on this, and it turns out it doesn't work. Touch surfaces don't want to be vertical. It gives great demo, but after a short period of time you start to fatigue, and after an extended period of time, your arm wants to fall off. It doesn't work. It's ergonomically terrible."
It's like having a remote control to read your kindle that's sitting on a stand 2 feet away (which, coincidentally, Amazon just announced).
Apparently the Ternus era of Apple is focusing on whether something can be built, not whether it should be released.