Graviman,
I don't think that EADS diesel-electric hybrid concept would be practical for an extremely weight sensitive application like a rotorcraft. At least not with power densities available in current technology electric motors and batteries. This type of thing looks good on a powerpoint slide, but once you get into the details of designing two complete propulsion systems (one electric and one diesel) you'll find that the weight, cost and complexity are not worth the benefits. A diesel/electric hybrid system only works well for vehicles that are not weight sensitive (like a tank or a locomotive) or for a vehicle that operates most of the time at a small fraction of its max power (like a car driving in the city). If what you want is reduced rotor noise then variable speed and/or high-frequency IBC (like Blue Pulse) is the right approach.
As for the merits of two stroke versus four stroke recip engines, that debate was settled long ago. On paper the two stroke would seem to have an advantage. But in practice, the four stroke gives better reliability, fuel consumption and lower emissions for an installed weight that ends up being equal to the two stroke. It's kind of like the old joke about turbine engines being mechanically simple because they only have one moving part!
Regards,
riff_raff