It's always fun to extrapolate, but hardest of all when very many dependencies are seen to be up for grabs.
Assuming that folks (think they will..) persist with One-car to fit all uses from 7-11 to SF --> Vegas - your guesstimate depends heavily upon prestidigitating a light, high capacity storage technology, at the very least. Hard to approach the energy/# of gasoline. Seen those numbers for ~ 30 years, now.
('Performance' places even more demands upon storage, of course.)
Secondly (we've had this discussion, so I'm just reiterating) - "hydrogen" and related solutions to sub-parts of the [energy - power/work - recharge] cycle, currently would rely upon the electric grid for part #3. Fossil, coal fired, NG, solar Primary sources just use any hydrogen they make (for ex.) as an accumulator/battery - with attendant thermodynamic %losses all along the cycle. We lose / Entropy wins.
Nuclear, with its plethora of tradeoffs (and a social-reluctance to deal realistically with its byproducts) is a whole nother thread; is obv. solely about Primary generation.
We May.. discover something Interesting, of course - but I seriously doubt it will be a New Law of Thermodynamics.
Alas too, as in-city housing becomes less and less affordable, and for the increasing legions of the displaced/outsourced holders of more McJobs: so is there no relief from the long commute in sight. So I see this seeming techno matter is entwined with the social matters we always neglect: er, 'inextricably'?
With close-in commuting: you'd have a small 7-11 + short commute all-electric vehicle. That, cheap enough that your Las Vegas cruiser (likely hybrid), seeing fewer miles/yr (lower insurance accordingly) - could make the 2-car compromise palatable. It wouldn't need to be replaced very often.
But: One car for all things + the typical commute miles (and Hours Wasted - big sub-thread) -- makes None of the currently visible/envisionable technologies look very promising to me - because Physics Rulez.
ie I think you're optimistic about it ending up "electric winning" - within ~30 years. (I have no idea what 'looks good'; partly because I believe that our fortunes thus options have been so damaged by Neoconman-think -- 30 year predictions even re this seeming just-techno topic are ephemeral.)
Of course we have to 'plan' something.. even while we determine if we can somehow ameliorate the vengeance of the massive Kill America group we've recently vastly multiplied and ignited. Plan... if we aren't too busy with the Unexpected (?)