The option to own a car with a CF roof in the entire US car market is so limited I see no logical reason to opt for the sunroof. Beyond weight, aesthetics, etc. this option adds a tremendous amount to making this car more on par with its more exotic counterparts.
As a side note, the last 6 cars I've owned prior to the M have all had sun roofs (including a panoramic on our Q7), and I think collectively I've opened them less than 20 times.
Carbon is King!! :-)