Mart,
IMO, the Interleaving configuration can never become viable until helicopter rotors have the ability to provide active and discrete pitch angles, at multiple zonal locations, about the combined disk area.
Active Blade Twist for the radial coordinate and Higher Harmonic Control for the azimuthal coordinate are a start; which can be undertaken today.
The Interleaving configuration should very likely become the optimum configuration for medium and heavy lift VTOL transport. Just consider that, the Interleaving configuration offers the advantage of a large disk area for hover, while also offering the advantages of short rotor-fuselage-rotor moment arms and fan-jets for high-speed cruise.
Nick,
Yes. Consideration was given to coupling the movement of the trim-tube to the movement of the cyclic stick. This would result in the hub springs only having an effect when the tip path plane was changed by an external perturbation.
It would have the advantage of reacting sooner than a fixed bumper. However, it's getting a little complex for a simple teetering rotor.