My guess is we will have both 3.0d (one turbo) and 3.0d (twin turbo)
In europe, X3 have both engine, i don't see any reason why we shouldn't.

However, the interesting thing is, some people said we might see the twin turbo gas engine like the one on the new 335i. If that's true, then we will get 4 different engine choice for 3.0L!! That's crazy.

3.0si, with 272hp gas
3.0 twin turbo with 300+hp gas
3.0d turbo with 231hp diesel
3.0d twin turbo 300+hp diesel