Super GTs in Japan uses silhouettes. The new Skyline GTR uses the same 350z chassis.

Silhouettes ensures more parity and easy to regulate and give certain cars extra help where necessary eg. Audi TTs in DTM, single template in NASCAR.

The problem with something like S2000 there's a grey area regarding homolagation. There was a huge fuss over the Alfa Romeo bodykits in early 90s BTCC because aero aids were forbidden. I'm surprised its been relatively quiet regarding VXR's front bumpers.