I'm not sure of the duration of the copyright for body styling or the amount of modification needed so as not to breach the copyright?
For example, the producers of the movie The Racers (1955) approached Enzo Ferrari about getting the loan of some racing Ferraris for their picture and Enzo turned them down. This surprised them as American auto makers routinely loaned or gifted their cars to film makers as a means of publicity. The producers responded by buying some used Ferrari and Maserati sports and formula cars, attached a different grill to them and called them "Boranos." ASAIK, the film makers were never sued by either Ferrari or Maserati.
Much the same approach can be seen in John Frankenheimer's Grand Prix (1966). Since much actual Formula One footage was used in the film, the movie cars were virtual duplicates of their real-life counterparts, right down to paint schemes and race numbers. Ferraris were dubbed "Manettas," BRMs were labeled "Jordans," and Honda was called the "Yamura." Obviously, Frankenheimer did not have a license from Ferrari, BRM, or Honda but I don't recall hearing about him being sued by any of the companies whose cars he copied.
Perhaps the issue is different with film because (1) the movie makers are not trying to sell cars and (2) an automobile is sort of a "public figure" as it is seen being driven out on the streets and race tracks of the world and, in a sense, is in the public domain.
Copyright, AFAIK, is intended to protect the expression of an idea, whereas a patent protects an idea itself (e.g. technology) for a much shorter period (18 years IIRC), and a trademark or registration is intended to prevent someone from producing a product so similar to the registrant's that the public might be fooled into thinking it was buying the trademarked or registered product. In the case of both copyright and trademark, I believe, the central issue is whether or not the consumer is likely to mistake the product for the real thing and buy it for that reason.
Thus, to my thinking, if the issue here is Ferrari's copyright of a particular design then a couple of factors may be crucial in determining the copyright protection: one, is PD's new expression of the idea (i.e. the Ferrari car) sufficiently different so as to qualify as a new, unique expression (like perhaps the grill and name change in The Racers) and, two, what is the duration of the copyright for a design that is no longer being produced? Certainly, PD couldn't model an F40 or Enzo and put it in the game, but what about a 1958 250TR Testa Rossa or 1963 250 GTO?
Possibly, PD could render older-model Ferraris and Maseratis and Lamborghinis and call them "Italias," for instance, and Porsches and call them "Rennsports?"
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Aww, I was thinking of buying GTR2, or even GTL...not anymore.
just expressing my gut feeling that it's very likely on a long enough timeline. And as long as there none of these monopolistic EA licences securing them right now, GT5 could well be the one! 
