I swear if BMW strays away from their inline 6. I'm going to become a Mercedes Fan Boy.
I get a sinking feeling that they will go to a V6 configuration, however. I sense that they will go with a single VGT snail mounted in the V with liquid to air intercoolers. This would keep the charge pipes (very) short and thus make the engine quite responsive.
I'd prefer that they get creative and mount an I6 transversely and use it as a structural member, much as V8s are used as structural reiforcements in F1 cars.