Indeed, we will have crossed a major threshold when EVs can generate their required electricity on board.
What we need is Dr. Emmett Brown's futuristic DeLorean that was powered by a "Mr. Fusion" reactor that ran on banana peels and other organic matter :)
It's not such a futuristic concept, though. You can separate out the H2 from a hydrocarbon fuel, like gasoline or E85 or whatever, on board. And then you feed that H2 to a fuel cell on board, and the electricity to electric motors.
You can do an online search and see that people are working on just this sort of scheme.
Since fuel cells have a hatd time with generating high current bursts of energy, a hybrid-sized battery is probably needed too.
Everyone is talking about EVs and HEVs, but Stop-Start vehicles provide a good interim means to save fuel and reduce emissions. We at CAP-XX agree that Stop-Start vehicles – with potentially more than 100 starts per day – could quickly kill a standard lead-acid battery in less than 18 months. Supercapacitors can support vehicle batteries by supplying the peak current (300A plus) for each engine start, enabling longer battery life. Check our site for tests we ran on batteries supported by supercapacitors vs batteries alone: Slides 3 – 9: http://www.cap-xx.com/resources/docs/CAP-XX%20-%20Supercapacitors%20for%20Automotive%20Applications%20%28website%29.pdf