First, a little history.
The Polonez is a family car that was produced in Poland from the 1970's until the turn of the century. In the '90's the basic 5-door hatchback body wasn't enough to stand a fighting chance in the new battle with Western cars, something slightly larger and more practical was in need. Before the factory woke up and started offering sedans and station wagons, a small company started selling 'expansion' kits: a new rear hatch which turned the hatchback into a wagon. The new hatch had a 'bulge' where the flat window would normally be, adding extra cargo space.
Standard rear hatch
Expanded hatch
As you can see from the pictures, the extension is very similar to a rear hatch with a Kammback, only it has a closed back and you can use the enclosed space. So by now, you probably know where I'm heading. How about producing a replacement extension hatch that not only gives you more room inside, but also reduces your car's Cd? It's just like the Polonez hatch, but the angles need to be tweeked. (I personally have never seen any information as to whether the Polonez's FE is better with the extended or with the OEM hatch.) This new 'aerohatch' would made for each hatchback or wagon model (or at least the most popular), be it Honda, Toyota, etc., replacing the OEM rear hatch. If built out of aluminum or plastic, it may save weight. The cost would be offset by the resale value of the old hatch door.
I got this idea when thinking about the unused space under the roof extension on my car, and seeing old Polonez cars hauling extra cargo under their extended hatches. What do you think? Does this idea have any chance of flying?