Erik Stinson in The Atlantic:

Nü Williamsburg dates back to a 2005 change to zoning laws allowing for the construction of new residential units in the areas of North, South, and East Williamsburg, semi-defined divisions of the sprawling Brooklyn neighborhood. In 2008, the housing boom busted, but, slowly, many of the then-new projects are being completed and filled.

But why does Nü Williamsburg need an umlaut?