One of the tests might be to check if there is good reinforcement in the area. Seems strange, but I thought that I read in one of the histories the lack of bootlid was structural with the unibody construction. Or felt to be. If this is true, then it stands to reason that the factory would add structure if they put in a lid.
I will dig around and see if I can find that history.
I am curious that you can see in the photo there is still the behind the seat pass through. I would almost expect that to be filled in with the addition of a lid.
The pics also look like a lot, is this example for sale?