Originally Posted by HongKonger

If they are flying DL it is now the only choice. DL's only flight to HKG now comes from SEA.

Don't count on an upgrade on this route or any other international route. As you noted they only happen when oversold, and then the priority is by medallion level and then fare class. A GM has very little shot at a UG on this route. But to give yourself a better chance ("better" meaning better than zero, but not much better), find a full flight on days that aren't common for business travelers.