You don't think the idea of "sub-classes" could work? I think it could, where the N-series system stays, but most events would limit players to a specific selection of cars within an N-series class. For example, an N100 race that limits players to kei cars. And when BoP is on but settings are disabled, I'd also prohibit "inter-class cars" - like how some N300 cars can go into N400 or N200, and so on - unless settings were enabled, either for all possible settings, or that particular section of tuning.