I see nothing ridiculous about it. Most PC workers are not glued to the keyboard/mouse - certainly not the keyboard.
I have tried the motion of raising my hand to do this and it feels quite natural, as long as the screen isn't too far away. At a trendy standing desk - which I am currently trialling - it actually feels quite natural.
Granted I wouldn't want to KEEP my arm outstretched but some use cases fit it quite well. I don't think it's necessary, but I think it has SOME merit - if someone can work out the kinks. And sorting out the kinks so it can be slick would suit Apple.