The Cadillac ELR will be a wonderful car -- for a two-door coupe. Here is the problem: I don't hear a lot people asking for two-door coupes. When people buy or see the Volt, they want the next car in the Volt family to be a minivan or SUV. Tesla has understood this with the Model X minivan, which will enter production only a month or two after the Cadillac ELR. Ninety-five out of 100 people with whom I speak about the Volt say they want a six- or seven-passenger Volt in minivan or SUV format, and with a lot of luggage space. They want a much taller car, so that an elderly person can slide into it without having to sit down as if crawling down into a Corvette. They want bigger doors. I have absolutely nothing against the Cadillac ELR. What GM should have done before the ELR, however, was to make a much longer and taller version, with three rows of seats, even with a center tunnel that would make it a two+two+two-seater for a total of six people. The car would be at least a foot taller. The battery size could stay at 16 kWh, and consumers would be prepared to pay whatever it would cost -- $59,900, whatever. The problem with the Cadillac ELR is not in the execution of the engineering. I'm sure it will be flawless and be the leader in its class. The problem is that it is a small class. What is the market for a $47,400 (and up, before tax incentives) two-door coupe? I imagine no more than 1%-3% of the market. On the other hand, the market for a three-row, six-seater version in SUV/minivan format would be a lot larger than 1%-3% of the market. As it stands, the Cadillac ELR does not expand the market much beyond the Chevrolet Volt, which is so good as it is. One really has to wonder: Who at GM was responsible for the product planning of this? Does GM not speak to real people, including the existing Volt owners, asking them what other car they would like to buy? Why is it that almost everyone one I know are praying for a "Volt" minivan or SUV, but GM runs off and makes a two-door coupe with tiny interior space? There is place in the market for a whole family of Volt minivans and SUVs in different sizes -- from six to eight passengers, from a lot of luggage space, to giant spaces -- but the room in the market for a two-door coupe is likely very small, especially considering the Volt is already in the market and is more practical. I look forward to driving the Cadillac ELR in 2013, but what so many people in the market are clamoring for is the same drivetrain in a much taller car that can fit at least six people and a lot of luggage. Think Dodge Caravan or Chevrolet Suburban -- with the Volt/ELR powertrain. At the time of publication the author had no position in any of the stocks mentioned.Follow @antonwahlmanThis article was written by an independent contributor, separate from TheStreet's regular news coverage.