Mart,
if it flies like a dream for 10 hours then suffers fatigue failure
Are you saying that 'fatigue failure' is not related to the problem of 'vibration', which was discussed above?
When X2 does fly, it will be a significant contribution to manned flight.
Your comment is a presumption, and hopefully a correct one.
However, it should be noted that many of the 'probable' improvements were recommended 25 years ago. Improvements such as; reduced twist, larger taper, reverse velocity blade profile, all composite blade construction, reduced parasitic drag, propellers for propulsion, etc., etc.
IMHO, the Coaxial ABC should be a significant advancement in rotorcraft. The question is therefore, 'why wasn't it's development continued 25 years ago?'
Dave