All the half-tonneau R&D expense for GM, Ford, and Texas Tech seems to have fallen on blind eyes.
I've never seen one since 1988 except the ones built for friends, or for Gale Banks Racing, and their land speed record.
Researchers may have figured that they were casting pearls before swine and gave up on any additional efforts to push the envelope.
The curve might have conserved vortex energy, allowing a stronger low pressure to be presented to the inner face of the tailgate, cutting drag further.
That's a good thought.
