I guess Osprey isn't an option then, which leaves us with making to best of a MASC version of Merlin or another rotary wing platform.
How much extra performance a modified Merlin would have compared to a normal one I don't know, can anyone give me a ballpark figure (in terms of altitude, endurance etc)? 20%? 30?
However I guess that installing the Sea King ASaCs equipment in a Merlin would be difficult. The rear cabin layout is totally different for a start. Then you have to ask would you need the radome in a bag arrangement, why not either use the existing Blue Kestral radome, or sone sort of array mounted on the aircraft underside?
So the conclusion is that MASC will cost money, whatever option is chosen. But perhaps we would be better of worrying about getting the carriers laid down, and worry about MASC when steel is being cut, welded and so on?