AFAIK, credits will not be used to unlock cars anymore, this includes S2 full aswell.
The credit system never worked as it was supposed to anyway, it was supposed to train people to use the slower cars before they got into the bigger/faster cars, but most people just found a way around it, like giving the AI crap sets so they couldnt move, ect ect.
The credit system anoyyed more people then it helped, i think.