Dave's wish for new ways to do things, and new capability for VTOL, is wonderful, and the work of the cartercopter crew must continue. The reasons why the ideas he proposes have not been successful in the past are quite explicable:
1) physics - the concept of an efficient hovering machine that also goes 250+ mph usually grounds out on the rocks of lost payload. Don't lose sight of payload efficiency in the hover, that's what we do, any compromise to this forgets why we were invited to the party. From tilt rotors to jump jets, to stop rotors and reverse flow rotors, the loss in hover efficiency has never been countered by speed. In other words, the product of speed time payload is what we seek, with a safe, fully controlled hover at each end. Anyone can make a VTOL go 500 knots, but it takes a very wise engineer to make it carry something useful, and do it in normal environments (wind and such). Real figures as to hover, cruise performance, and cost are quite scarce, so far.
2) money - The DARPA/NASA/Sikorsky X wing reached no fundamental engineering limits in its tests years ago, nor did the HLH. They ran aground when they ran out of money, and showed returns marginal enough to cause the moneybags to close the pocketbook. (Remember what caused the cancellation of the original Star Terk? ratings - money - the one monster Kirk could not defeat.)
3) mania - It takes a wise designer to keep preconceptions from screwing up his design. A campaign to rid a design of a feature (tail rotor, wiggly blade) must be undertaken because something better is found, not because these things are inherently ugly. Some of us seek metaphysical harmony, not engineering sense, and this can cloud judgement. Seeking tailrotorless symmetrical rotorcraft for their own sake is not the game. Making practical, monitarily justified machines that work in the real world is the game. The cathedral of Notre Dame has the marks of centuries of structural patches on its buttresses, evidence of the hodgepoge of fixes and claptrap that from day one been used to keep it standing. Those designers were not embarassed to try some screwball fix, they did what it took to keep the enormous space within dry and warm for its occupants. Remember the old adage - if its stupid but it works, it is not stupid.