Sounds like the way Superformance (of South Africa, IIRC) does business. They ship incomplete cars which lack only engines, transmissions and radiators. You roll it out of the crate and into your garage and drop in the powertrain of your choice. The cars are otherwise finished - the paint is done, the brakes are bled, the upholstery and carpet are in. Currently, their products are of a certain type:
However, I could see a more utilitarian vehicle offered in the same way.
Of course, if the kit-car trend ever made a significant dent in the U.S. vehicle market, there would be a barrage of legislation aimed at killing it. You know... airbags, door crash beams, that sort of stuff. Just one or two items off of the long list of federally-required new-car safety features would be all it would take.