How says S65 vs. S55 is only an no sence discussion ... should only take a look at the poll results !
1/3 of the voters says that they would pay an
extra ~10T€ for getting an S65 with the old M-DCT this mean ~6T€ only for getting an unique engine with round the same hp- and lower torque-numbers, but an totally different and more traditionally M style power delivery characteristic.
And I bet, if such an option would be offered from BMW M Performance (Individual), it would be sold in numbers big enough to make no loss or a little profit.