Thanks for the great pictures, DHP.
We've been looking into an i3. Our research provided the answer that BMW has no plans to offer a rack for the car. So we concluded that we'd carry one or two bikes in the back when needed. Our measurements confirmed that this would work, but your picture, well, is worth a thousand words.
One trick: we also carry one or two bikes in our VW Golf (fairly similar dimensions (the Golf is slightly larger) in back with the rear seat folded). We stow a black, folded, bed sheet in the back of the car. It's light and folds small, and any grease from the bikes doesn't show due to the color. If we need to carry two bikes, I spread the sheet out on top of the first bike and put the second bike on top. Not much padding but it seems to work to prevent scratches. The black sheet is also handy whenever you want to carry something dirty or dusty and want to keep the car clean. Easier to shake out and/or wash the sheet than the car.