Kinda funny, people spend all kinds of money on the newest car design, ceramic bearings, special shocks, lightened gears, lightened axles, etc. etc. etc. but want to mount a billboard on top of their car.
Put your hand out your car window at 30 mph and see what happens.
It's also funny how people spend all of this money on top of the line safety equipment and then mount their kid to where limbs or even heads stick out of the car. I wouldn't advise it either.
I guess the moral to what I'm saying is. People do odd things. But, I don't see the problem with people running visors. It's not hurt anyone's performance but their own and there are things legal in our sport much more dangerous.
Given the right tech specs and limitation I just don't see where it would be that big of a deal. But, I guess I'm not USAC. Their organization, their decision I guess.