I think so much is dependent on the HK situation.
Seldom does DL upgrade inconvenienced OAL revs (I've seen partner revs move up --prob medallions)
I know the policy is not but flexibility at some point has to be responsibility of gate agent. No one really wants to leave any nonrevs when there are empty seats, but I don know some agents who just clear who they can last minute to get the flight out.
Guess that doesn't definitively answer the Q, but I'm hoping that if we need our AF zed seats last min JNB/CDG , they put US up front!!