[pierrec]

I wonder if a touchscreen version is doable using the frustrated total internal reflection technique [1]. Relatively cheap projects have been done with that technique, but never with a mirror, AFAIK.

It's somewhat different since it requires a sizable box behind the surface and an internal projector instead of the screen. As for turning it into a mirror, it might be as simple as adding a two-way mirror under the Plexiglas pane (or possibly between the pane and the diffuser layer). But this is where experimentation becomes necessary!

[1]: http://cs.nyu.edu/~jhan/ftirsense/