Yes, rally cars is a direction that this game can really explore. What about a set of buggies, maybe one RWD and one 4WD?
A NASCAR type car would be great as well. You would actually have to let out of the throttle on the oval for a change. A car with this kind of weight would also be quite a challenge on the road coarses.
A sports prototype would be just awesome, somethings much smaller than the GTRs.
I believe that LFS's niche is that it is a comprehensive racing game. What other game simulates road cars, GTRs, formulas, rally racing, oval racing, drag racing, etc. as well as LFS. Because of this, I really don't want to see too many real life cars. If the developers had to model real cars, their jobs would become much more difficult because they would have a strict standard to adhere to. With generic cars they can easily balance out weight and power and car classes without haveing to worry about a perfect representaion of a real life car.
In summary, what I would like to see for this game is:
-More Rally Cars (buggies)
-More rally tracks (maybe a whole map devoted to several different on and off road configurations)
-NASCAR type stock car (more ovals)
-Sports Prototype
-Some really short Karting tracks for the MRT.