Interestingly, Porsche have just announced they are bringing out a manual version of their latest 911 (992 model) with a 7 speed box. Acceleration will be less than the PDK - around 4 secs to 62mph rather than 3.2 secs! As if that matters for the ordinary owner. What matters more is the fact that they are offering a choice. They would not be doing this unless there was a considerable demand for a manual.
I agree that it might be impossible for MMC to offer a manual with the Plus 6, given the 8 cogs and power available etc., but if they were to bring out a CX chassis Plus 4 with a manual box I would be very surprised if it didn’t sell more units than the Plus 6.