Surely it's the kit and the operators that are the most important thing, so in the absence of many alternatives to a P8 perhaps equipping the C130 or A400 with the appropriate kit is a possible. I'm not talking about role equipment, I'm talking about permanent installations in noise resistent cabins for a dedicated LRMPA aircraft. I don't think that the Harvest Hawk kit is really relevant for a true MPA.
Lots of compromises, I know, but the P8 is also a compromise.