The P-8 is indubitably equipped for boom refuelling, down to a matt-painted panel above the windshield to keep the sun out of the operator's eyes.
Exactly why, I don't know. The kit had been developed and paid for under Wedgetail and it may have been considered valuable for certain missions and heavy/high-drag configurations (such as carrying a
ing big radar around).
Also, it's interesting that the MoD graphic indicates (lower right) that the P-8A will be tasked with counter-volcano operations.