If only we could see the designs! Fisker designed the Artega GT, the Atlantic and the Karma (among his other designs at BMW/Aston Martin). Btw, if the Karma were the original design for the Model S, you'd have a lot more usable storage space and room. Rather than the battery tunnel in the cabin, you'd have a flat pack beneath the feet. Instead of the limited trunk space in the Fisker Karma, the "Tesla Karma" would have the much smaller electric motors with integrated inverter which would free up another 60-70% more trunk room. Oh yeah, and there's the ICE - which, if this were a Tesla pure EV, would not exist - so the "Tesla Karma" too, would also have a "frunk."
Regarding the Cd of the car, the Karma's is 0.31 is admittedly worse than the Model S' 0.24 but still great by comparison to, say, Ferrari's sleekest, the 458, which is 0.33 and even the "efficiency drives design" Toyota Prius which is 0.30. Also, given the ICE of the Fisker Karma, its drag coefficient is affected by the vents needed to cool the ICE. As Tesla noted with its active air flaps, the Cd can be greatly reduced when those flaps close, leading one to think that if the "Tesla Karma" had no such ICE need for cooling, it would also benefit from a lower Cd. Just my $0.02.