Some people here have had it done. My dealer says it isn't available yet. As for gains, it would be the same as on the 550i, which is a 6 hp gain over stage 1. Not a lot, but it is supposed to improve turbo spool up off the line. On my stage 1 there is a slight lag before boost hits, so I'd imagine they worked this out.
Stay tuned, there is a stage 3, 4, and 5 on the way. Prototypes of stage 5 on the 550i are supposedly making 560 hp and 600 ft lbs of torque.m
2011 Nissan GTR Red/black - HP Logic tune/midpipe - "Lightning"
2012 BMW X5 50i M-sport Dinan S1 Space gray/black - "Thunder"
2012 BMW 550i M-sport Jet black/black - "Black Cloud"
Gone but not forgotten: '12 X5M, '07 AM SuperVantage, '05 Boxster S, '01 BMW M3,...