Porsche Manufactur insiders have revealed that a convertible version of the Panamera is coming up, and it will have its two rear doors dropped to increase chassis rigidity, making up for the lack of a roof. 
Porsche also wants to minimize the weight of the extra chassis reinforcements needed, which would swell up if it also had to make up for the fact that it had four doors.
Porsche also wants to minimize the weight of the extra chassis reinforcements needed, which would swell up if it also had to make up for the fact that it had four doors.