Unable to download NASA pdf of control system analysis, but yes it was ahead of it's time. It certainly demonstrates that a cost effective hingeless gyro is practical. Maybe even manouvreable.
I think part of the difficulty with modern hingeless rotors is that the rotor frequency is so much higher now, due to the higher speeds and lower rotor mass. This means that any rotor eigenmode is comparable to the rotor frequency, so there is inevitably lead angle required in the pitch link. Although the tip radius was quite small, those tip heavy blades would likely have all sorts of interesting modes.
Actually, there are days when i catch myself wondering whether you are right about laterally seperated rotors. It would push roll reaction times way down, since heli does not have to pendulate to new equilibrium. I have even pondered about smaller control only rotors, like Sikorsky's early VS-300! But these days a good SCAS control system can response shape the cyclic input to get a reasonable response. I think keeping the cost and weight of the machine down is more important.
It will be interesting to see how the X2 development engineers overcome the difficulties if the envelope is pushed above 250KIAS. Clearly active tip control will become critical to avoid blade divergence. I would be curious how much higher the blade 1st bending frequency is pushed too. So roll response may approach that of fixed wing...