If the leftist idiots didn't have fits at the very thought of diesels, we'd have diesel-electric cars that could probably get better mileage than most Gasoline-powered cars. Diesel-electrics are old and proven technology, and have been used in trains for decades. Imagine, a diesel engine providing electricity to a vehicle while running in its optimal power and efficiency band. None of the loss from starting, stopping, and shifting gears. You could buffer it through a reasonably small battery pack.
The Audi A3 TRD 1.6 offered in Europe got 74.3 MPG.
But of course, they despise small diesels.
And that was pure Diesel. A Diesel hybrid could probably get 85 mpg.