How about a mirror that is only there when you need it? The car could detect from a combination of your eye movement and from its own monitoring of the road beh

How about a mirror that is only there when you need it? The car could detect from a combination of your eye movement and from its own monitoring of the road behind when you are likely to check the mirror, and pop it out then. This sounds like a lot of overengineering - you need reliable low latency eye movement detection and a motor mechanism that can react that fast but withstand the air forces at highway speeds. Just to deliver a worse UI - imagine the complaints about how Tesla doesn't detect my eyes unless I look just right. But 6% fuel usage sounds like an enormous saving that would be worth some of your complexity budget.