In The Innovator's Dilemma there is an analysis from the 90s presented about when pure electric cars would be economically viable for a mass market. Based on then-current technology projections, it would happen around 2020.
The critical combination that their analysis found necessary is price below a certain level, sufficient acceleration to merge into an Interstate, sufficient range, and fast enough recharge time. The Tesla currently fails on price and recharge time. It over-delivers on power, and has about the right range.
Hopefully, by then we'll also have Li-Air batteries or more viable ultra-capacitors (which Elon Musk thinks are the future for electric cars).
Also, Better Place has an interesting business model, similar to the one of carriers subsidizing phones, by subsidizing electric cars to make them cheaper upfront and then having to pay a few hundred dollars per month to replace your battery at their stations whenever it discharges. I heard it's already gaining traction in some Middle East countries and also in China, and they plan to expand in some European countries, soon.
Will electric vehicle cells follow the same curve? If not, why not? Is it because they contain precious materials? Lack of economies of scale? ???
In many very different industries for a long time, once there was an agreed upon and measurable criterion for "better" they delivered exponentially improving performance for periods of decades. What is exceptional about transistors is the rate of doubling, but not the general shape of the curve. (More normal rates of sustained improvement are 5-10%/year.)
Lithium-ion batteries have been on a sustained path of improvement since the first commercial ones were released in 1991. If that curve is projected forward to 2020, you hit a price-performance point where electric cars are likely to be competitive.
Incidentally if the history of innovation is to be trusted, I would not look for the first successful mainstream electric cars to be from major auto makers or from companies like Tesla. Successful disruptions tend to come up from the bottom of the market. Look at companies like Club Car that sell things like electric golf carts that are already appearing on the road. It is much easier for companies to expand upmarket than it is to strip products down. There is no reason to believe that this has changed.
The trick seems to be that the company who establishes a high-price and high-margin product needs to be willing to cannibalize their own sales with lower priced offerings.