If I were building an airplane with 4 gas engines I would run 4 Tech Aero IBEC units. Reason being is that they can all be driven off the same channel so if needed you can shut down all 4 engines at the flick of a switch. You would also be able to run 2 redundant RX packs of whatever chemistry you desire and that's all. I know you expressed the desire to not want to run wires through the wing but if you think about it, wouldn't that be better then running a separate battery in each nacelle?