Actually a great idea, especially for multiple bikes, front wheel, back wheel makes for denser storage and simpler than alternating the height of the hooksActually much easier to hang by the back wheel. (Idea cribbed from Scotrail bike storage on trains)
Pick up the bike by the frame, both hands share the load, hook the back wheel. Better than having the front wheel waving about trying to hook the wheel without scratching the car, or wiping your trousers over the filthy car.