I'm sorry, but some of you are running away with this story beyond what it actually is. If you wish to read the original report directly, rather than rely upon Autocar's report of it, see it here at Auto Motor Und Sport:
http://www.auto-motor-und-sport.de/news/wirtschaft_-_handel/hxcms_article_516418_13987.hbs
The main thrust of the information elicited by interviewing the BMW Development Director by AMS magazine is the continuing discussions by BMW and Daimler on the joint purchasing of parts, systems, whatever, which are not obviously brand identifiable. The subtext of this is BMW and Daimler need to counteract VW's 6 million+ a year purchasing contract muscle in order to competitively produce A/B classes and 1/3 series cars especially, not to mention Toyota's c.10m unit purchasing stength and even PSA and Renault's roughly 3m units each. Jointly, BMW and Daimler have no more than 2.5m units to offer to suppliers to lower economies of scale.
As to Mercedes throwing the towel in on engines, forget it. There's mention in the AMS report of joint use of BMW's 12 cyl. engine. That's it. Even this I doubt will happen. Daimler, realising the gravity of the economic collapse taking place, would not see a V12 engine option as particularly vital right now, even with Maybachs or top-end S class's. With oil and gold headed for 50+% and 30+% falls respectively even the billionaires of the Gulf States, Russia and China - by dint of no longer being able to flog piles of junk to bankrupt West - are all feeling the pinch and demand for plutocratic V12 limousines will drop like a stone. It's back to the pre-80s I'm afraid.