And yet there are still 6 locked slots (which have now been removed...)
I'm thinking Retro DLC, which is likely to be, and better be, free:
Mini Cooper
Datsun 240z
Old Jag has been mentioned in a hands on
Aston Martin DB5 or similar also mentioned somewhere previously
hmm...
I think they just added extra slots to keep people on their toes. They did the same thing with the tracks.