The problem is the material dictates much of the design. For FTIR to function, the curvature of the clear material must be such that the angle of refraction causes the light inside it to bounce back from the surface internally instead of escaping, like a superball in a narrow hallway. This means you need both a material with a high refractive index (i.e. Poly Methyl MethAcrylate aka Lucite/Plexiglas) and a shape that propigates the light beam. This then will dicate the overall design of the mouse.
Which means features such as handedness ergonomics will be difficult to do with this design. All the existing designs on the market would need to be modified to accomodate it. The process and materials involved in attaching the lightpipe to the base may not be easy or cheap. The shape they use at least in this demo will have issues with the front wanting to drag from the low area of contact with the desk relative to the pressure. And since it's a brittle material, I'm betting that thin arch with nothing supporting it will crack from stress as it ages, rendering the mouse useless in a much shorter time than users fine satisfactory.
Buy an acrylic cup from the supermarket and use it. See how long it takes it to develop the first cracks. Now assume any crack over 1mm will cause a diffraction of the light beam rendering the whole thing useless. I'm betting an optimistic 6 month product life is not ideal for a mouse.
Oh and the fad for "green" everything will hate it, since PMMA takes twice its weight in petroleum to produce.