PD have to make all the cars premium if they are making GT6 for PS4. I guess graphics will be better on PS4, and they can´t have standard cars there. But I´m not sure they will release too many cars as DLC on GT5.
If PD are smart, they´ll release both cars and tracks as DLC to show what they are doing when the next GT is coming out. I hope you understand what I´m trying to say. Getting late here...