...but with so many innovative new hingeless rotor designs out there I would challenge whether this is really an issue.
Graviman,
Those "innovative new hingeless rotor designs" present a whole new set of potential issues. One has to wonder why the X2 spent relatively little time flying (around 22 hours total?) before it was consigned to the museum. One possible reason may have been the "innovative new hingeless" coaxial rotor design. In some of the videos of the X2's high speed runs, I can recall seeing the downward deflecting retreating side blade tip of the upper rotor passing very close to the upward deflecting advancing side blade tip of the lower rotor. While the X2 blades are fairly short, this problem will get more difficult as the blades get longer.
riff_raff