A buddy of mine mentioned this idea and I thought it was absolutely brilliant. Adjusting stances has made Arma 3 a lot more realistic. If you want to avoid fire, you duck your head, right? If you've ever seen a movie with someone driving a car and someone is firing at them, what do they do? They duck their head down into the steering wheel to make a smaller target. I absolutely think this should be eventually implemented in the game. I'm not sure how many stances would be necessary. I think two is enough; regular stance, and adjust key + down to lower your head into the wheel. The advantage would be that you're a smaller target, and the obvious disadvantage being that you can't see the road as well.
The only issue I can think of this would be third person view. Would people take advantage of it and constantly be in the lower stance to be a smaller target, but then drive in third person mode to see the road just as well? The solution to this could be to only be able to lower your stance in first person view, but then you're limiting your gameplay. It's a tricky situation.
What do you guys think?