Here in Belgium you have the rear seats taken out of any car and register it as "lichte vracht" (light cargo), massively reducing the taxes you pay on it. Anyone can do this.
I've actually considered removing the rear seats from my Ford Fiesta simply for the increased practicality, was mostly just deterred by the hassle/expense of installing some kind of cargo floor to replace the seats.
I've seen an Audi RS6 like this.