It was to have a small ICE from the initial design. The first 40 miles might be all-electric drive. If you live close to work, you could save a bunch of money on fuel. Of course the computation includes the additional electricity that you would buy, but electricity is very cheap compared to gasoline.

A few years ago, we used a generator for a week. The thing took about 100 gallons of gasoline to produce less than half of the power that we would have used, sans the outage. I know that a car engine is more efficient, but the generator costs a lot to run. The fuel cost almost $300 for one week. That's more than we usually pay for a month's worth of electricity.