Hang on Dave, you saying all helicopters would be made out of folded card? Gonna meet son of single rotor pioneer in a couple of weeks, so i'll mention it. Exciting stuff BTW - you know what they say about meeting your heros.
Seriously, for this thread lets assume that the two technologies had been developed side by side
. Clearly X2 is where the two meet, so you could say there is already a convergence. If intermeshing had been standardised helis may have achieved higher speed sooner, but may have suffered in sidewards flight. From the handling point of view symetry is good, but single rotor control systems have evolved to produce linear rate control (SAS, AFCS, FBW etc). High rotor hub separation gives a fast response, but then so does high effective hinge offset. Efficiency of two systems is in practice probably similar (although a paper only exercise could probably prove otherwise).
On balance, i think when an engineer is confronted by contraints of cost reliability and performance he/she will go for the simplest solution to deliver. To my mind MR/TR is that solution, but it is not without compromise. As market expectations shift so will the required compromise, and i will be interested to see how X2 affects this...
Mart