Both SFO-HKG flights are pretty empty in business class on the 29th. The morning flight having more space than the evening one.
You could book coach and then pay the buy-up offer when you check in. The sum of your coach ticket plus the buy-up will be less than $7k. Note this is different from the buy-up offer you’ll get at ticketing (that will likely be higher).
If you don’t like the cash upgrade offer you could just apply miles and co-pay at that time.
The risk to this strategy is if a flight cancels before you get confirmed in J your flight could fill
up with refugees from the impacted flight and leave you back in Y.