Well here are 2 suggestions. First, I think it would be a good idea to have working interior components for vehicles such as clocks, interior lights, and also an option to open and close the windows on the cars. Second, I think that interior components such as plastics should realistically deform and crack on impact.
I'm gonna be Gabe's psychic here and say 1. Already done or WIP ^_^ (I'm really hopeful on this one) and 2. We're working on it No, noobs: I have no idea where the Development state is -_-
This would such fps like crazy if engineered at all like the other body deformation. And it doesn't actually make anything more realistic physics wise...