In all seriousness, there are numerous Japanese cars that (IMHO) should be premium (or even in the game) and aren't.
Quick list of cars that don't exist even in standard form:
Nissan: S12 and & S10 Silvia, any Cedric/Gloria, any Leopard, Pulsar GTI-R & VZ-R, any Cefiro, 2nd gen Primera.
Mazda: Any Mazdaspeed edition car other than the 6 concept, 323GTX, MX-3, MX-6, RX-2, RX-3, 1st gen RX7.
Subaru: XT, Loyale GT
Mitsubishi: Eclipse GSX, Starion
Toyota: Mark II
And for the 500th time...the "30 Skylines" amounts to a total of 4 or 5 different in-game models with minor variations. Not the same thing as 30 unique models. And there is only one duplicate premium GT-R within a generation (the '07 R35 and the '09 R35 SpecV).