Presumably the limit to platform sharing will not go as far as sharing old platforms or drivetrains from old Mercedes-Benz models on new Chrysler vehicles, as was done on the 300C (pictured above) or Crossfire.
Mercedes is also including new Eastern European and Asian suppliers on its new C-class sedan to help reduce costs. This is a risky move considering the recent (and ongoing) quality issues suffered by Mercedes vehicles, but obviously the company claims no quality will be lost by using cheaper suppliers.
The Volkswagen Group is one of the most prolific companies to share platforms and engines between different brands. The same platform/engine combination may be seen in cars from Audi, Volkswagen, and Seat and the company is often accused of simple badge engineering.