Good point. However, I don't anticipate any changes to the structure itself. What I was referring to was the "frame" that goes around the door windows. You can see the difference if you look at the hatchback/coupe doors and see that metal frame above the actual door, whereas the convertible doors don't have that. They just have the door.
Maybe that metal frame does add something to structural rigidity, but I don't know. Hmm...You've brought up a very good issue I will have to deal with first. If this is solve-able with subframe connecters, those are in the works anyway! :p