Dozens of automotive models—from manufacturers that include boutique supercar makers in Europe and mass producers in China and India—may never roll down U.S. streets. Once the unquestioned destination car market, the U.S. is no longer even the world's biggest. Last year, China became the top consumer of motor vehicles. Our list this year includes two cars we'd like to see here: the world's fastest pickup truck and a two-seat roadster with a roof that retracts in just 12 seconds. Nevertheless, you won't see these vehicles in a showroom any time soon.