[aerohead]

A pure highway vehicle would have to be idealized for low drag since that's where the load is.
Up until recently,GM was the world's largest automaker and basically dictated how the industry would work.
And since the late 1920s,GM has been dedicated to 'variety'-selling,the annual styling change,and design obsolescence,all the creation of GMC under Alfred P.Sloan Jr.
In 1963,Walter Korff of the Lockheed Aircraft Co. was promoting real aerodynamic auto design and presented at the SAE Congress that year.
Paraphrasing one response to Korff, in the 'Discussion' section of his paper, is precient remark made by H.Schmude of GMC who asked of Korff," If all cars were designed 100% streamlined,would they not all look alike,and designers have nothing to do?"
It appears that,short of tectonic changes in consumer values,that we're stuck with what I refer to as,Trash & Landfill Design Studio mentalities,whereas,at the introduction of each year's new cars,the designs for those cars have already been trashed and in the landfill for at least three years.
As long as function takes a back seat to styling,I see no possible significant improvements that can be made,otherwise they expose the hand they've been holding for 90-years.