Not only that, the plane you'd catch at JFK routes JFK-YVR-HKG- so availability on JFK-HKG should mean availability YVR-HKG (unless CX is really weird about married segments or something).

That being said, in theory JFK and EWR are coterminal, so using AS to go to EWR means you can catch a JFK flight. However, saver F availability SEA-EWR is very iffy, so you might end up flying transcon in Y just to fly back to YVR again. The only way I'd see wanting to do this is if you wanted the NYC stopover (since I believe AS awards allow for stopovers at the AS gateway), or you just like being on planes.