The key to the success of these things will be the ability to get information from the display without having to touch it. At first I figured this would mean an always-on display (so, e-ink, I guess), but this clearly isn't that, and yet they don't seem to turn the displays on in the videos (though I'm sure they're all fake).

I wonder if you could do something with the accelerometer that would be good enough? Like, if your arm orientation changes to look-at-your-watch position, the display turns on, and it turns off again when your arm goes back down to your side.