You cannot use GUCs on MU. I believe you can on KE, but you have to pay full fare(? someone correct me if I'm wrong?). DL has plenty of connecting options from NYC to PVG to be able to use the GUC on DL metal. DL recently ended their only flight to HK so it cannot be used there. Lastly if you did a mixed itinerary something like NYC-DTW-ICN-HKG/PVG, you could use the GUC on the TPAC portion if it were on DL metal.