You guys make some very compelling arguments about why we're unlikely to see a 400Z convertible. I think you could well be right.
But at the same time, lots of people were speculating the new Z would be a shooting brake, or electric, or that there would not be a manual transmission offered, or that there wouldn't even be a new Z at all. It's really impossible to predict for sure what Nissan's going to do.
Here's some more speculation about a new convertible:
https://www.topspeed.com/cars/car-ne...-ar189604.html