A more likely theory is that this was GM's first mass-produced electric car, and it would take almost no sales from other GM products. GM rightly assumed that 95% of Volt buyers were coming from a non-GM car. Therefore, almost nobody would postpone the purchase of an existing GM product in order to wait for the Volt.
Yet, at the same time, the Volt was so "out there" that GM somehow didn't think the competition would be awakened to go down a similar road. The market for plug-in electrics was effectively zero until the Tesla (TSLA) Roadster in 2008 and the Volt and Nissan Leaf in December 2010. Sounds far-fetched today, but it was what our world looked like 2007-09.
The Volt has now been in production for over three years. Typically, the work on a new car is started at least a few months before the old one enters production. In the case of the Chevy Volt, that would have meant 2010.
However, since the Volt was such a dramatically all-new car, and the development was rushed to an unprecedented degree, I think we can assume that the work on the Volt 2.0 didn't start until 2011. Using conventional metrics, we can assume that the Volt 2.0 won't enter into production until some time around the middle of 2015, presumably as a 2016 model.
So what's different with the Volt development this time?
For starters, we don't know anything about it. Nothing. Unlike the last time around, GM has not shown a prototype, not a "final production design," not talked about it at all except in generalities so vague so as to be meaningless: "A future Volt will be better in every dimension we can" is how you'd summarize anything reliable GM has said.
The most specific information came from former CEO Dan Akerson, and those comments were so all over the place one that wonders whether they were deliberately misleading, mysteriously uninformed (by the CEO nonetheless) or whether he was outright drunk when he made them. I guess the only thing that was 100% believable was that it was going to be cost-reduced so GM could finally start to make money on the car. In this case, cost-reduced doesn't necessarily mean "price-reduced."
So why is GM so secretive this time, when it wasn't last time around, 2007-2010? The answer is twofold:
1. There is a Volt 1.0 GM needs to sell. If you haven't been paying attention, the Volt 1.0 hasn't exactly been flying out of dealerships. GM has been selling 23,000 per year in the U.S., and not that many more internationally. If GM told us about the Volt 2.0, sales of the Volt 1.0 would likely collapse.