I love that concept. When I first saw it, I thought it was an aviation technique called "Dope and fabric covering". But then I saw the doors opening, and such. So it's still a flexible fabric after all.
I don't know how that would hold up at speed, and deform between the support structure for that matter, making the design look rather odd i bet.
If it was 'doped' fabric, it would be very taut and hard, much like a drumhead, and would hold up to speeds very well. It is used on light aircraft very successfully in this manner, on everything except engine cowlings. And those planes go over 100 mph.
As far as the inevitable tears in the fabric. The aforementioned airplanes use a modified baseball stitch to close the tear, then a piece of fabric is doped on over the sewn area, edges pinked. The only other alternative is to re-sleeve the entire section.
Love it! Makes me want to build a car like that.