Looking at the launch on the M3 in the UK I think it suffered quite a bit from only having the 6MT transmission. A lot of SMG E46 owners wern't taken with the new car on their test drives.
My bet is to prevent the same happening in the USA market which will account for 50% of all M3 sales, that all (strictly limited) M-DCT production will go there until June production at the earliest.
I was tempted to wait for DCT but it seems pointless taking delivery late July when the reg changes 1st september in the UK, so I'm sticking with 6MT.
In terms of cars they make I heard a figure of 100k over the lifetime which works out at say 15k a year, about 250-300 cars a week. Was SMG 60% of production on the E46 so to meet demands they will need 150-200 units a week and far more over the next 6 months to meet launch demands.