Believe what you will but the discussion was not about weight to strength, Mg alloy make up, its about the strength of the N52 to withstand F/I. The head guy at BMW says no. Its really that simple. You can talk to you're blue in the face about heat treatment and all buts its not going to change that fact. Were talking to blocks here that have already been produced not what ifs. And when the production manager for all BMW I6 engines says the N52 is not suitable, its fact!
Why they went to an all aluminum block, I have my opinion about strength of the blocks and Im not thinking cost is an issue at all. BMW put the Mg/Al block in many thousands of its lower cost models. If it werent an issue, Mg/al blocks would be used in all the powerful more expensive models, M division for one. The fact that the Mg/Al block wont be in any BMW models next year speaks volumes also. You can come to your own conclusions, I did.