Listen to half of you, its all just guessing or assuming stuff you know nothing of. On the above do you think PD (its a company by the way with 3 other Directors not a single man) do "Concept Car" designs for free or as a business agreement? What i can say for fact though is on the "Collaborations" webpage showing all the cars since GT1 the calender goes upto 2009 so their will be more to come even if youd expect this at least the timeline has 2009 already on it.
GT5 will have a alot of surprises and improve over GT4 in many ways, we dont know the details but we will some day, jumping to conclusions all the time though doesnt help.
Things to look forward to and confirmed:
Top Gear Track (Exclusive)
Ferrari
Car Clubs
Home Intergration
Weather
Improved Physics
Improved Track enviroments
Lots and Lots of Cars
Lots of tracks
Damage
Photomode
Thats quite a nice receipe for a tasty racing game dont you think?