I can see where it would lend itself to a smooth profile design - but what about doors with styling or functional 'features' in them? For instance, earlier Mustangs with the scoops, or even more dramatic - say, something like a mid-80s Ferrari Testarossa with the "cheese grater" air intake scoops in the doors that actually make them 2 or 3 times 'thicker' than normal doors?
The Lincoln Mk VIII they chose for their prototypes lend themselves well because of the smooth and fairly rounded design profile of the doors. Be interesting to see how they handle something more 'stylish.'
As well, I have to agree on the Lambo doors - interesting enough, but they really only work well on Lamborghinis. Coming up with a kit for just about every car out there kinda cheapens the novelty, if you ask me.
I'm also more partial to gull-wing doors, like the ones found on early Mercedes 300s and DeLoreans. GM prototyped some gull-wing doors on their 'Aerovette' that split in the middle of the body line and folded inward (keeping with gravity) that kept the swing profile very close to the car, eliminating the need for lots of space on either side of the car to get them open. Now those were cool.