Its a 7% share swap, most likely to co develop certain technologies. Its not a merger of branding whatsoever. I will doubt that it goes through, but even if it did, nothing will change with either brand other than for example; they share a similar variation of a hybrid drive train or some other new technological platform. Its not as though everything BMW will be made in concert with MB.
Its a market hedge in the event one company does bad while the other does well, the company doing bad at least benefits from their 7% stake in the other.
Its not the BMWapocalypse people