It's interesting how people old enough to remember the old diesel technology think that today's automotive diesels have not improved. That's a very capable car. It weighs close to twice what its predecessor weighed, yet still gets the same mileage. It's not designed to be an SUV or a land yacht, it's a new kind of car, designed specifically for high mileage with an internal combustion engine, and is being presented as such. The limitations are not being hidden or suppressed. Keep in mind that the same kinds of arguments persist with cars like the Prius, which has been successful, popular, durable, reliable, and capable during its production history. The Prius is still considered new fangled by many, but it's been in production, for sale, for about 15 years. The Tesla model S also has limitations (more severe than the XL1), but that doesn't prevent them from selling a lot of them to satisfied customers.
What if, for example, the XL1 concept could be extended to get less fuel mileage, like only 200mpg, but with a more comfortable cockpit and air conditioning? That reality can be achieved with current technology. You gotta give these guys some credit.
Consider, for example, how the XL1 reconceptualizes the meaning of the phrase "fill up". Today, a fill up at a gas station means buying 12 to 20 gallons of fuel, for most people, and that amount of fuel is typically good for about 300 miles of travel. With the XL1, a fill-up means buying 2 gallons of fuel for 600 miles of travel. Does that not count for something?