Do you buy the premise (or perhaps the conclusion) that the energy stagnation of the past ~50 years is one of the key reasons why “the future” hasn’t yet been realized in the way that one might have assumed back then, had we been more willing to use the required amount of energy to produce and sustain those innovations (like flying cars and nanotech)?
The future very rarely goes the way we predict.
That said, I never thought that flying cars were a reasonable expectation for the near future, mainly because the failure modes are terribly bad and keeping them from happening at intolerable rates is incredibly expensive. Even if we were very rich, they were powered by Mr Fusion, and piloted by infallible software, occasional mechanical defects alone would make them not something I’d want to use every day.
We do have nanotech already, just not the “build everything for free” magical wish fulfillment nanotech. More energy wouldn’t have helped that much, there are lots of very real problems at that scale that we still know little about solving. We may get further toward magical wish fulfillment nanotech in time, but it will take a lot of brainpower not horsepower.