I think the reason it has never been attempted is because the coupe's large rear C-pillars block most of the inward view. Most people have tinted windows, so the tint would obscure your view of it unless you drive around with the hatch up.

From the side, it wouldn't be readily visible unless you tilted your seat forward... and, there's nothing behind the seat we need on a regular basis.

On a roadster, this would be a great mod because the seat backs are visible to motorists behind you.