They would start with a Model
They would start with a Model S frame and make a two door. It would still be a full size car. It wouldn’t make sense to take a Model S frame then modify it to midsize, that’s too much money and they’d charge Bentley money for the car which would defeat the purpose. I wouldn’t object to a Model 3 convertible for that matter either. If it’s going to be midsize just make a Model 3 droptop.