All of the complexity of current-day cars is driven by the automakers. If this is mandated as a requirement from the government, they won't be permitted to charge us much more than the $100.00 per car it would actually cost them (service parts are 10x manufacturing costs). Think of all of the garbage on current cars right now. I'm particularly fond of the laughable refrigerated cup-holder option, or the tire inflation sensors.
Realistically this doesn't have to be integrated to a greater community than a 1/4 mile radius around the vehicle. I would hope even more that there were no user-interface components at all, but rather a warning that around the bend are three stopped cars in the middle of the road...
More information is helpful. It just needs to be tailored to suit the situation, and it shouldn't necessarily be shared with the driver unless it is helpful. We already have more than enough distractions behind the wheel.