How about a visor on the car? I'm thinking of a windshield that's high enough to extent to about the top of the driver's helmet.
if you look at the Surtees crash it sort of dropped onto his head. not like Massa's where he went into the spring.
FM's accident would have been a non-issue. And who knows maybe the wheel that hit Surtees would have been slightly deflected by a windshield and thus, at least lessened its devastating impact?
indeed, we will never know, but on the other side of the coin how many people might get hit by something deflected of it?
if they do not want a vistor/windshield, how about a slit like a tank. but then I am sure people will complain it would not look very good