Well, you cant sell a million copies with just obscure cars that nobody knows. I m fairly sure they are trying to get the well known british manufacturers (Jaguar, Aston, Lotus, McLaren) licensed and I m certain they are trying to get at least Audi, as there are some fake-Audis in the game already. VW is also a good guess, as they were mentioned in the career design draft. I m sure SMS will also try to get some other important and lustworthy brands who have racecars or sports cars that fit well into the career mode. Mercedes springs to mind, Lambo, Chevy and we know that they have been contacted by a large german manufacturer (my guess: Opel). Besides that, my personal wish would be some Alfa and Maserati goodness.
But we dont need to tell them, they know all this as its been thoroughly discussed at WMD over the last year.
PS: Damn, how could I forget the Aston GT3?! Very high on my "Me wantz!" list!