This would be a step backwards
The iPad lets you touch stuff. This is direct interaction with your data, near enough, and that has to be the ultimate goal in computing.
That's not possible yet with 3D. If the UI is behind the screen, you can't touch it because there's a piece of glass in the way. If it's in front of the screen you can't touch it because there's only air where you see the image.
Because of that, I can't see this happening until somebody comes up with a method of doing touchable 3d.