I did a little bit of reading on this and this is my take:
There is definitely an exemption to crash testing for low volume. It covers ADR 69, 72 and 73, satisfied by a seatbelt labels and placard warning the occupant (same as ICV). You can read about it here
RVCS MENU under administrators circulars number 0-2-13.
A cobra would be eligible for entry to the SEVS register because there is no full volume vehicle available to the market. Caterham 7 is on the register and sold as low production.
As CMY-427 says the cars would have to be built the same except for variations in colour and minor trim changes. You couldnt choose motor type, brake combinations, suspension etc.
Realistically how many turn key complied cars would actually sell? The cost of these cars for it to be worth while for the manufacturer would be in the high $100ks and then they would be having to sell and market them much the same as a car dealer, perhaps they would need a trader license as well, show room, test drives, more insurances etc etc and they will be limited to how many they can produce.
This kind of defeats the purpose if you cant make it your own. Also a kit is a much cheaper option. Many of the people on this forum (including me) wouldnt own a cobra if you had to buy it as a complete production vehicle costing $150k - $200k.