It's possible (indeed virtually certain) that insurance types will factor in the expected value (positive or negative) of a given feature. They already evaluate expected costs tied to more nebulous associations between a vehicle and risk (Does model X get stolen disproportionately frequently? Are buyers of model Y, in midlife-crisis-crimson possibly not the most cautious of drivers?); if assisted braking or rear-view cameras, or lucky rabbit's feet, reduce the expected cost of insuring a given vehicle and operator, they'll presumably be folded in. How much of any savings the end users sees may or may not be an exciting number; but that'll be more about relative bargaining power.
I suspect that reductions in legal requirements are less likely. With things like BAC, people are already pretty tepid judges of when they've actually had one too many, and keeping the test equipment and testing environment calibrated, reliable, repeatable, and adequate as evidence is a fairly big pain. Even if we assume that all the relevant laws are 100% about public safety and have absolutely no secondary purposes (which is a matter of some...doubt), those aren't conditions that are going to endear some tiered system of caps based on a the car's feature matrix to anyone. Purely informally, effective input stabilization, assisted braking, and any other tech that keeps your car moving in a nice respectable, not-drunk-looking, way even if you are a bit sloshed will probably reduce your risk of being pulled over and tested, and thus effectively raise the limit a bit (except at the delightful 'sobriety checkpoints'); but if they don't mask the effects well enough to avoid attracting attention, I'd bet that the legal results will be the same.