Let me just chime in.
I think what Rasmanac is talking about is being able to shape cars more freely. Let's say you represent the car's silhouette by a curve. I can now add points to this curve and freely move those points around, thereby affecting the car's shape. The resulting curve is then translated into polygons by the game. There should be only few restrictions, say for example some less curved space for a windshield, a minimum roof length, etc. This is of course just for the silhouette. For other parts of the car, I'd love to simply pull on e.g. the edge of a window frame and change its shape - or add and remove points defining its outline, then freely moving them around. Adding to that, many cars have inward or outward indentations on the sides, which are IMHO an essential component of car design. A first step in this direction would perhaps be possible in the way of modifying some of the grills - there are already "blind" ones, that don't actually provide air flow and just add a fancily shaped dent. This alone would enable things like what the
Hyundai Veloster uses to accentuate the lower part of its doors and its tail lights.
The current way of designing cars, at least judged from the demo, feels extremely restrictive. You are constantly fighting the controls and the limitations instead of expressing your ideas. We can change very few parameters of some blocky, extremely low-poly pre-designed cars and then add detail in the form of lights, grills, door handles, etc. Adding detail is actually the part of the car design element that works best (I love the lights and grills - there is a nice selection and they look brilliant), although controls are still very clunky, especially once you are laying design elements on top of each other. I'd love to have copy and paste elements I've placed down or groups of elements, I'd love to be able to place any element anywhere, e.g. attach a door handle to the boot lid. There should also be some kind of quick save function, allowing the user to experiment a little, select a few components, save the selection, modify them and having the option to return to the saved selections if the modifications didn't turn out that well. The current revision mechanic is a nice idea, but it affects the whole car.
I've only played the demo so far and currently, the car design element feels like an underdeveloped afterthought compared to the complex, realistic and extremely fascinating engine design element. I know your game is still in a very early state and I'm sorry if my words were a bit too harsh. Your game is unique in the current market, full of innovation and it definitely shows a ton of promise. Once it's on Steam, there will be few things holding me back from a purchase, despite its flaws. However, if the car designer doesn't see a major overhaul, I don't think I'll spend much time with it compared to the engine designer.