I am with Doc all the way when it comes to Big Iron vs anything new. The economics and ROI just do not add up. I have 3 cars - all 16 years old. We scraped up enough money to pay EIGHTEEN HUNDRED (not thousand) dollars for the last one. The Eddie Bauer F150+, which is the smallest size that I can own and still pull my assorted trailers, has 350 THOUSAND miles on it -- and I only paid $10,000 for it 275,000 miles ago. The Taurus Station Wagon with 165,000 miles on it was $18,000 new. I drive the Sable Station Wagon with 140,000 miles on it about 100 miles a day at up to 80 MPH and get 21.5-22.5 MPG! What is my Return on Investment? It has to be incredibly low.
Where are the real breakthroughs? I don't care what George Clooney, Arnold S, or Jay Leno can afford to buy and manage to get to work in. The American people need solutions that support the hundreds of thousands of cars already in existence. Solutions such as trees in Brazil (Popular Science circa 1965) or other genetically bred yeast or other plants that produce that produce Diesel fuel, Gasoline, or Jet Fuel directly (NASA Tech Briefs, March 2012). What about using turpentine from pine trees to produce oil (south Georgia, 2011)?
As to complete replacement of existing cars, it will have to be something so major the we are willing to throw away all of the existing, functional, existing machinery. Like Doc says, "ain't gonna happen." And by major, I mean cantaloupe sized fuel cells or cantaloupe sized Nuclear powerplants! Or even, something completely unknown... And, no matter WHAT it is, what are the odds of the EPA allowing any of it to happen.
There is always a chance. I know all of the scary possibilities of a hydrogen/oxygen explosion or a radiation spill in an accident, but, hey... Ours is the same government that MANDATES an explosive device IN FRONT of your FACE!