I have always hoped for factory options, TDU was a mean taste test to this (and it tasted fantastic).
You made a post in the News thread wanting more in the dealerships than just selecting car colors. It developed into a short idea discussion which I rather liked. In short, the dealerships would offer the usual car selection and colors, but then you could also juice up your purchase with basic performance options to upgrade your car to an extent. Things like wheels, intakes and mufflers, fuel system upgrades, turbos, brakes, etc.
If you wanted to go further, there was Tuner Village where you could get much higher performance upgrades, and even produce a specific tuner version, such as an Amuse S2000 or HKS Skyline. You could even get some livery painting and decal work done. And for full blown racing modification, there was Racecar Valley, or... whatever you'd call it.

There, you would have some extensive - and expensive - body work done to bring your car up to spec to qualify for SCCA, BTCC, Rally, DTM, Super GT or whatever class of racing you wanted. Blank race cars we could paint up would be good too, either way, I'd be happy.