From the autoweek aritcle:
"Even at high speeds the M3 GTS remains wonderfully flat and neutral during cornering, and with the DSC (dynamic stability control) switched into M-mode, there's rarely any intervention."
So, we know it has MDM, but we still dont' know how it is activated (unless I missed it somewhere in the article). I suppose it would likely be via the same setup that is now rumored to be in place for all M3s as of 2011.5. I.e. you now get MDrive standard and can now configure it via the computer in the guage cluster (no need for IDrive). Actually, this would make the appearance of the system for 2011.5 on regular M3s more rational - they already had to develop it for the GTS, so why not make it available for the base car.
2008 Interlagos Blue E93 M3 - M-DCT
2011 Salsa Red Jetta TDI Sportwagen - DSG