Looks like the previous rumor of a partnership was just that, a rumor. This quote from the latest Automotive News (Sub required) says it all:

>Thomas Weber, head of research and development at DaimlerChrysler, told Automotive News Europe on Friday that, “There have been no discussions with BMW on sharing platforms. Although I would never say no.”

[ Mercedes and BMW not working on A-class follow-up ] Automotive Green

[ D/C and BMW not talking about cooperation for A-class successor, top executive says ] Automotive News