This is not as far along in development as the X2 but here is an interesting idea from Boeing for a similar aircraft. I wonder about the extra weight of the retraction disc, mast, and ducted fans, and the wings do not look very strong either, but maybe it could be made out of composites. This one looks a bit more expensive than the X2 but it should not be a lot more and you could mount armaments on the wings.

And we thought the V-22 was complicated and expensive...

With the ducted fans it could probably go faster than a V-22 but not by much unless it's supersonic which I seriously doubt.

Collier Trophy Goes to Sikorsky X2

(3/17/11, Aviationweek) Sikorsky Aircraft and the X2 Demonstrator Team have won the 2010 Robert J. Collier Trophy “for demonstrating a revolutionary 250 knot helicopter, which marks a proven departure point for future helicopters,” the National Aeronautic Association announced March 15.The Collier Trophy will be presented at the 100th Anniversary Collier Dinner, this year on May 5 in Arlington, Va. Other nominees were the Automatic Ground Collision Avoidance System Fighter Risk-Reduction Program team; the MC-12W Project Liberty team; the Orion Launch Abort System Development team; the Boeing C-17A Globemaster III team; and X-51A WaveRider team, as well as general aviation’s contribution to “saving thousands of lives in Haiti.” Sikorsky flew the self-funded X2 technology demonstrator in 2008. The United Technologies company plans to fly two X2 light tactical helicopter prototypes in 2014, and has talked in terms of 2017-18 for an S-76-size commercial high-speed vehicle.