First, I think this is a neat idea.
Second, the "WAF" is humorous and indeed important; I dread the day when I go to a large EM gathering and my wife gets together with other wives/girlfriends for a group rant.
I do have one criticism. This would be best suited for a much larger, less aero, vehicle. I am doubtful of the FE gains you will see from this, and the added utility/safety will be nearly the only gain from this mod - maybe not enough to pay for itself.
I do empathize with you; I criticize Honda, Toyota, and SMART for chopping their cars too short. Adding another foot or two at the back gives you some aero benefit, increases cargo room substantially, and has the potential for HUGE gains in rear-ending safety. Instead they want their cars to be easy-to-park for people who can't drive. The Honda Fit and the SMART fortwo are the worst offenders - no cargo room, wasted aero, and no crumple zone!