The Voyager KC3 can refuel the Sentry using the FRU, but as the only A330MRTT variant not to have a boom, the Voyager cannot refuel the RC-135W or the P-8A. Surely such a lack of capability has been addressed?
...or the C-17 or even the Voyager itself, and while the UK doesn't currently have plans for the F-35A there has been talk of a split-buy for those operations that don't need to be flown off a carrier. No AAR capability for those either, though.
The sooner they address the boom-on-the-Voyager issue, the better really.