I never really though about this, until I just looked at a Model X picture after reading the 5/7 seat poll. Without the 3rd row how will it be prevented that stuff just falls out of the trunk? Has there been any demo showing the rear seats folded down? Is there a car with a similar setup? Looking at other 7 seater SUVs like the Mercedes GL or Audi Q7, the setup usually looks like this. Basically the 2nd row ends where the door starts so there is no space behind the 2rd row creating a gap at the door.