An automaker that builds on a unique platform can market the car differently from a similar-size combustion-engine version of the model. That will be important given that — for a few years yet, anyway — the expense of the battery pack will price electric models higher. VW is already doing this.

"The Modular Electric Toolkit jettisons all the ballast of the fossil age," VW declared in its marketing. MEB, it said, led to "fundamental" changes for everything from body design to interior packaging.

Meanwhile, an EV on a flexible platform could inspire unfavorable comparisons to its cheaper combustion-engine version.

But VW isn't the only one investing in EV-only platforms. Daimler is working on the Electric Vehicle Architecture, or EVA2, which is expected to reach the market in 2021. Two sedans and two SUVs will likely use it first.

Meanwhile, Renault-Nissan-Mitsubishi is developing the CMA, an electric-only, flat-floor version of its broader Common Module Family architecture. It is expected in 2022. And in Japan, Toyota is working with Subaru on an EV-only platform it announced in June. No timing has been given.

EV-only platform designs with the batteries sandwiched in the floor present their own problems. The batteries raise the height of the floor, reducing rear foot space, as a quick test of the ID3's rear seats at Frankfurt revealed. And in vehicles in which the battery box's size pushes toward the edges of the structure, more crash protection is needed.

"In a side impact, you have a very limited zone of deformation to the battery — about half," said Niclas Brännberg, director of computer-aided engineering for the Chinese EV brand Nio. That means extra stiffness, meaning more expensive extruded aluminum beams for Nio. But Brännberg, who previously worked for Volvo and Saab, estimates that the cost of developing an EV-only platform is similar to that of a combustion-engine platform.

VW is way ahead on cost with MEB, said Sudowe of Gestamp, which builds battery boxes and chassis parts for vehicles using that platform. "MEB will be the benchmark for everyone," he said. "It's very good on the price perspective." For example, all MEB models except the minivan will use the same control arms, saving money on dies.

Sudowe estimated that MEB is around half the cost of the EV-only platform Jaguar Land Rover developed for the Jaguar I-Pace.

The I-Pace platform, designed as a halo car to beat Jaguar's premium rivals to market, is not expected to be further developed. Instead JLR will migrate models to its new flexible Modular Longitudinal Architecture starting next year. The first model to use it will be an electric version of the XJ large sedan.