The idea of using a UAV as a weapons carrier certainly has merit ('Pony' lynx/wasp/seaking?) and is not a new concept. Perhaps an issue not considered so far is maneuverability at low level. With acoustic ranges being what they are on modern subs, laying tracking patterns is quite a split arse type of flying and I'm not sure a vehicle designed for endurance at high level would be capable of that? Dropping weapons would be possible but tracking and aquiring an attack solution would be a challenge!!
At least it would stop everyone blaming the f*****g pilots for making them sick again...