I'm almost surprised that BA doesn't use HKG as a sort of Asian hub with fifth freedom rights since the Brits basically built and paid for the new HKG airport shortly before the handover. OTOH they do have CX as a oneworld partner, while there isn't a *A or SkyTeam partner with lots of service at HKG. Similarly UA could use fifth freedom rights to operate more intraAsia flights. Also, AFAIK there's no JV between CX and BA, which is a but surprising as coordination would seem to be potentially beneficial, with BA able to deliver lots of connecting passenger from Europe, just as AA could deliver them from the USA to CX.

It's disappointing that fifth freedom doesn't cover mainland China from HKG as CX tends to operate flights to mainland China using affiliate carriers rather than mainline full service CX. Even though it's a logical routing and would avoid the mess at either PVG or PEK (or CAN) one can't easily use HKG as a connection point for destinations within mainland China unless you're willing to transfer to LCCs or limited service affiliate carriers.