My list would be:
1: No bugs in my vehicle workflow yet.
2. I’d love a wizard for vehicle creation. I’d love to see a dialog or window that prompted the import of vehicle chassis, what the body is, assign tires, and how should the suspension behave. I do this often enough that I know the processes and can do them basically with my eyes closed, but to have this automated (I don’t really know how to build tools effectively, and I’m not at the point where I want to create/test/implement my own tools) would be just fantastic. Particularly when controlling how movement priority should be handled, and even moreso for streamlining line traces to materials for tire track creation. That’s just a pain.
3. I’d prefer ease of physics configuration over realism to a point. If easy configuration comes at the cost of physics realism (adjust these four values to makes the physics you want! But, it’s not going to be as accurate as Gran Turismo!) I’m Super Okay with this.
4. My primary interest is in creating mostly standard vehicles - road and offroad stuff. Not like rock crawler kinds of things, more along the lines of rally cars, with my target audience being kids. This is why ease of implementation is key, and hyper-accurate physics aren’t critical. I need to be able to put new cars in quickly to react to demand, and as long as they react predictably the physics aren’t going to be judged harshly.