Likewise, this technology just projects onto on oddly shaped object. It doesn't magically add any of the depth feeling that you get from, for example, watching a movie with 3D glasses.
The reason this is so difficult is that when you view a real object, it reflects light in all directions so that your eyes actually see two different images when you look at it from two different angles (your two eyes, or any other arbitrary viewing angle).
Imagine that you were trying to make a projector that no human would be able to distinguish from a real window. Imagine that you had the requirement that the user would have to be able to look in different directions out the window and get different views just like a normal window would. What you would have to do is create pixels that can project different colors in different directions and maintain complete control over which color was projected in each direction. In short, you must create a pixel that will look different depending on which direction you view it from.
If you think of it this way, you basically would have to control each pixel as a series of subpixels, each subpixel pointing in a specific direction. To make it realistic, you would probably need thousands of subpixels for each pixel, increasing the requirement for number of pixels by thousands of times and decreasing the required minimum size by thousands of times. Also, you have to make the subpixels point in only one direction.
And that, my friends, is almost impossible.