Musk is probably privy to near every speculative R&D firm in electrical energy storage - likely regularly. For 15 years to have 1/2 of vehicles electric, means the disclosure / productization of some speculative battery / capacitor advance is fully in production in less than 7 years, likely needs to be in full production in 3-5 years from NOW. Whatever than means regarding a speculative new technology ( that enables a significant cost breakthrough to validate his claim ) is self evident. Given all of the Arpa-e projects, it will be curious to see which advance is causing Musk to get so giddy?
I think you've got the right idea spritoo22. In 15 to 20 years the largest market for cars will likely be in places like Shanghai, Mumbai, Jakarta, and Sao Paulo. In these large developing cities a very small and inexpensive electric "city car" could be a big seller. The US and European markets may be much smaller than the developing world in terms of number of units sold. So Musk could be right.
Is some one here, just going to say NO ? OK i will, it is not going to happen, No matter how you advance the talk of this, it just isn't there, unless Cities are redesigned, and you know the mess major cities are in now. Sugar coated Baloney about Electric Cars, has to end. it will be a micro market in the car industry.
Interesting concept, although even there, you need to store (heavy) hydrogen, as the fuel. So really, not that much different from the fuel cell approach, as far as ease of fuel storage.
Although it may not work well if you expect a hydrocarbon fuel to hold the hydrogen atoms. (Is there a lot of dueterium in hydrocarbon fuels? I think the main source of dueterium is sea water?)
The bottom line being, to me, there's no reason to get fixated on a battery as your main energy storage medium, to qualify as "fully electric." Even if a smaller auxiliary battery is used for transient high current demands, similar to mild hybrids.
Does this mean it's time to invest in nuclear fusion for electric power generation? I want a Tesla sports car that contains one of those Mr. Fusion home reactors like Doc Brown had on his DeLorean. According to the movie, that happened in 2015, so I guess we only need to wait 3 more years!
Read this 1959 Fortune article about the space program. They predicted a man on the moon before Kennedy called for it. Almost everything they predict happened.