CoffmanStarter,
It makes some sense that the P8 cannot do AAR. It is a Navy Asset when in US service, as far as I am aware the USN and USMC do not have any boom equipped tankers.
It would seem strange to me if the USN wanted to be able to AAR the P8 that they would want to rely on the USAF.
I cannot see the UK needing to do longer missions than the USN will no doubt be doing over the Pacific.