A live view from the rear camera would be awesome as it's going down the road.
Add in the needed front camera view (displayed over/under) and you can check on the driver's activities both coming and going.
This is also great for parking lots. Not only to see who is checking out your car but if you park across from some chargers that are full, you can periodically check for openings from wherever you are (work, mall, park) and go and plug in when you see a spot opens up.