Mercedes selling that motor as a weight saving benefit is absurd. Mercs have always weighed a ton more than equivalent vehicles from other manufacturers, and it's that weight/solidity that makes them drive the way they do. An S-class at 130mph feels safe because it weighs as much as it does (I have done that in my more reckless youth). A C-class weighs 50% more than an equivalently sized VW Golf (I've owned both); it's only the weight/solidity that makes the C feel safe(r). So IMO to make any Merc lighter-weight to make it more economical undermines the very market they're in.
But then Bloomberg reported yesterday that Tesla sold more electric vehicles in Germany over the last 12 months than VW, Merc, BMW and Porsche combined.