as it would have been known that receptacle-equipped aircraft existed and that there was a chance that the RAF would at some point over the 27-year FSTA private finance agreement perhaps acquire and need to refuel such equipped platforms
Mel, not strictly true. It was always assumed that UK programmes needing AAR would have specified a UK compatible P&D refuelling method. This was the case with FSTA and both AirTanker and TTSC were looking at how a probe could be fitted to their candidate aircraft to allow buddy-buddy refuelling of 'FSTA'. Again the requirement for FSTA to be able to 'swap spit' was originally in the programme but traded out because of the PFI implications. Stupidest decision ever if you ask me.
C-17 wasn't in the equation as they were only leased and supposed to be an interim capability.