Steve Trimble over on The DEW Line reveals Boeing has a DARPA contract to study a disk rotor high-speed rotorcraft. Like most things in aerospace these days, this is not a new idea.
Swiss architect and designer George Vranek, on his diskrotor website, traces the concept of a circular rotor with retractable blades back to Germany in 1962 and also mentions a 1992 NASA Ames study.
US engineering firm owner Frank Black has tried for years to find backers for his Modus Verticraft concept, and now Nowegian firm SiMiCon is working on a retractable-blade disk rotor UAV.
They all see the same attraction - the ability to hover like a rotary-wing aircraft then retract the blades to fly fast like a fixed-wing aircraft. They all take slightly different approaches. While Vranek's concept has conventional rotor blades, the Modus design has a larger number of shorter fan blades. 
Some concepts drive the disk rotor conventionally, and need an anti-torque mechanism. Others would duct engine exhaust to the disk's periphery to drive the rotor, avoiding the need for a tailrotor. SiMiCon's UAV is steered by moving the centre of rotation of the circular wing. All need a powerplant that converts from driving to rotor to propelling the vehicle.
It will be interesting to see which approach Boeing takes. DARPA appears to be funding a number of different advanced concept studies and its endorsement is far from a guarantee of success. After all, Boeing and DARPA had to abandon the Canard Rotor Wing after both demonstrators crashed. Maybe the disk rotor will have better luck.