I think it would be great to see this implemented, including the engine rocking when revved in neutral (and the resulting torque on the body through the engine mounts / etc.) This is a subtle effect in most cars, but this whole game is basically about modeling all the subtle physics effects that other games ignore, and it's the combination of all those effects that make it so visually realistic. In cars that are softly sprung (like the Roamer Off-Road), in real life you would definitely notice the torque applied by the engine to the frame/body. When you're talking about trucks, the transmission-differential torque is pretty important for accurately modeling their behavior. See this video for an extreme but real-world example. It would be great to see this effect in, for instance, the Gavril Cement Mixer. It would probably not get the tire off the ground like in the video, but nevertheless in a game striving for realistic physics I think this effect should not be ignored!
