The problem is that an EWR flight would be just for local residents. I don't know what demand is like, but could that support a daily flight to HKG when there are 4 daily flights next door?

It would be great if CX could do EWR, perhaps even convert CX888/CX889 to HKG-YVR-EWR-YVR-HKG.... and add a direct flight to replace that at JFK. But perhaps that would be too much capacity to HKG?

CX can only get Oneworld connection of usefulness from EWR to: DFW (Its better to fly via LAX) and MIA. Thats why they currently fly to JFK for all the AA connections.