Dave,
OK, maybe intermesher is less of a compromise than i thought for sideward flight. Certainly it has the same, and possibly greater, advantage of coaxial for compact powertrain. I understand that if you chose a config already championed you will lose the initiative, but it sounds like a good horse to me!
Appreciate what you are saying about interleaver not tilting, but powertrain will not be that much simpler. The driveshaft has to be able to take the full engine torque from one engine to the other rotor for OEI, potentially during high roll manouvres, and this has to be seen as a full reverse torque fatigue loadcase. This means that driveshaft will need to be large diam and will need many intermediate bearings, with surrounding structure, to avoid shaft resonance. Chinook, or tandem in general, powertrain might not be a bad place to look. This means that outlay and running cost pushes machine into transport applications to get the return, so we are not talking about a privately owned machine with this config.
Appreciate what you are saying, on site, about same diam (hence mass) rotor reducing disk loading on interleaving over coaxial. I think you need to do a separate study to understand how much of a compromise the increased width of the machine will be. Dedicated transport destinations will be able to cater for a wider config, but there is a definate market advantage to being able to squeeze in to a landing site. The hypothetical risk is you then lose out on sales for machines which can get into tighter spots, since future coax manufacturers (like 'sky) would simply increase the rotor diam to stay competetive. In weight terms my guess is that increasing rotor diam by 30-40% is lighter than the extra pylons and driveshaft mass, and this still lets coaxial be 20-30% narrower. Just something that needs consideration.
Mart