Mart,
The following is a little off-topic but you mentioned
"X-shaft + gearboxes in the interleaver eats up a bit of payload" and slowrotor mentioned
"small independent electric motor".
All-Electric Intermeshing UAV:
The weight of outrunner electric motors is very light therefore the 1/2-scale UniCopter UAV below is designed with 3 separate <20 hp motors at 4.2 lbs each. The electrical power would be provided by on-board batteries or a central engine+generator. The only gearing is a single 2-gear set at each of the two rotors, and no gearing at the propeller.
Click for large view of the above drawing.
Then click on magnifying glass mouse pointer, for larger view.
Dave