I have a thing for 1960s F1 cars like in "Grand Prix Legends." I don't have that game, but apparently the year is 1967, and you're piloting these beautiful old race cars with skinny tires. From when I played the demo with a choice of a few different cars and Watkins Glen, it was pretty interesting to have to wrestle around with fast (in their day) cars on skinny tires. If PD really wants to get into the nitty gritty of vintage racing, they'd include some of the old F1 cars even before F1 was even coined. I can imagine having that six-wheeled Tyrell as a Prize Car you can win. My next question, then, would be if actual F1 teams will want to actually be in GT4. It would be interesting to see the companies in GT games to have their F1 cars represented (if any). Examples of teams who created F1 cars or F1 motors would include Ford (actually Cosworth), Honda, Renault, Mercedes-Benz, Peugeot, Audi, Alfa Romeo, just to name a few.
Outside of F1 cars and on to one-make customer single-seaters. A nice One-Make series race would be if Suzuki featured their Formula Hayabusa. I think I had it in my [only] volume of Import Tuner which featured the Formula Hayabusa. It's a bit of $30K that could do 175. In fact, many of the single-seater open-wheel makers should have some of their machines represented. You know, Star Mazda, Formula BMW (such a thing?), Formula Nissan, Formula Holden, all-out.
But to sum up my calls for open-wheelers, mostly 1960s F1 cars, single-seaters from even before "Formula One" was even coined. Dig? Good.