Mart; you mention;
"Unfortunately development of X2 seems to have ground to a halt, which is a great shame."
Perhaps there are problems developing appropriate airfoils for high-speed flight. In addition, the two rotors and the propeller are all in very close aerodynamic proximity to each other.
Recall that the nighttime promotional picture of the prototype showed a fuselage etcetera but no rotors or propeller. One would think that Engineering would develop and test the complexities first.
Perhaps this quote from the AHS Rotary Wing History thread says much.
"Perhaps his [Igor] greatest accomplishment was in his skills as a showman in selling the helicopter to the military, ...."