I think people may interpret the "spirit" differently. I don't think any guy off the street can go and "buy" the Cyber Evo's undertray/splitter combo off the shelf. To use your example, look at Tilton's front end. I'm sure you can buy it from them but it's hardly "off the shelf". Same goes for RE Amemiya's RX7, rear mounted cooler, wide body, hektik diffuser. The concept of being able to "buy" it is loose anyway, you can buy anything with enough money. If you mean off the shelf then a lot of former TA cars are also disqualified from running concept/prototype parts or making one off bits to suit the car - though technically you could still buy those parts with enough coin. I get what you're saying though, we were used to see stock bodied/lightly body modified cars running great tyres and suspension with huge power, but now people are getting into crazy aero, customising suspension and chassis geometry and the like in the search fo seconds and it's not something the average punter can do - which is why they have specific classes to address this.