There is a tri-turbo petrol version as well. I've known about BMW's R&D on this version for several years now, and it's highly unlikely that it will not come to fruition.
Originally Posted by mkoesel
I believe that the engine being referred to here is the existing tri-turbo diesel.
There is still no firm evidence that a tri-turbo gasoline engine will see the light of day. Thought it does remain a possibility.