What made A bodies non-popular

After thinking and thinking, and looking at other cars, I came up with an idea.
If you look at the tail light panel of a 70+ cuda` or a 70's Roadrunner, or a charger, the tail panel dips in.. and on most A bodies, it bulges out, so I have the idea to have my tail panel custom made to where it dips in. Using the same tail lights, same body line, just an inch or so in. Then I want to find some trim, or make, to go around it, so I can paint the intention flat black and the the rest of the car another color.

Does anyone else think this would give a Duster or Deamon/Dart Sport a "Sportier" look?