Yeah, my friend/sales rep told me he heard that it was going to be a reality.  He even referenced this spring.  I'm still waiting for that Performance Pkg. to arrive here in US for the 545.  If I were BMW I would definitely bring that 550 to market along with performace pkg.  That powerplant could put the 0-60 performance in the 5 second area, assuming weight of engine is not significantly higher.