There are a couple of things we know with certainty of as today. Google is a corporation. It has to maximize the value of its stockholders. At the same time, it has to balance the various moving parts of Google's revenue/profit generating apparatuses to maximize returns and deal with out factors like competitors and partners alike.
When Google made the announcement to buy Motorola, the response was lukewarm at best from HTC, Samsung, and Sony. Even though Google has assured Android partners it will not compete with them and will keep the Motorola division at arm's length, everyone knows when push comes to shove, Google will look after its own interests.
What its partners want to know are what are those interests? Continue to generate ad revenue from search via Android? Sure, definitely. What if Google finds that it can also doing quite well or better by selling phones? That is what partners are afraid of.
Hence, the problems of what to do with RAZR and other Motorola brands. Nexus is likely to play the role of being the model clean Android device, devoid of third party skins or carrier inference. RAZR is unlikely to play the same role as the Nexus. Google doesn't need to two devices that does the same thing.
What Google is likely to do is to allow Motorola engineers to continue to develop hardware and perhaps get rid of the skin and run RAZR and other devices with pure unadulterated Androids. They'll have different designs than the Nexus devices which could be made by other companies. And this will give Google the security of knowing that there are devices out there that will continue to sport Google apps that will still generate revenue for Google.
Yes, they'll be competing with the Galaxies, Ones, or Sony's Android devices but RAZR and other Motorola devices will be very different in that they won't have customized skins.