Right...because we haven't wanted better batteries for the past 30+ years, and it's just our lack of desire which is keeping it from happening.

SpaceX didn't do any new science in building their rockets, really. They took functional technology and a lot of great engineering and made it work. I don't think it would be responsible to bet Tesla's success on a battery technology which doesn't exist yet; 50% cheaper Lithium-Ion through Tesla/SpaceX style vertical integration and awesomeness is good enough.

If better battery chemistries come out, then sure Tesla could use them, but the planning for the next car needs to work even if they don't.