although i don't believe bmw will introduce 5.6L onto E70. however, i do believe that bmw need to up their engine lineup to compete with Mercedes and Audi.

Mercedes basically put AMG on every model. bmw doesn't have anything compete with cars like S-class AMG, ML-class AMG, SLK AMG.. etc.

even Audi has things like RS4, RS6, RS8. i am sure bmw will not want to lose in the horsepower game. (especially the core value of bmw is speed and handling)

my guess is that BMW didn't see the horsepower game coming so fast. They almost have nothing to compete and the twin-turbo 3.0L patrol engine feel almost like a afterthought. However, i expect someone with the "motor" as their middle name is working hard on the next generation engine right now to compete in the next round.