I was on HKG-DFW recently and I had only booked it 2 days prior in Y. The J cabin was "half empty" according to an Agent, and the seat map made it look more like 75% empty (but of course this is not the best indicator).

About 24 hours prior to the flight, they appeared to have processed the upgrades for most of the list and left only 3 open seats in J. I was not upgraded. That means there were ~30+ EXPs (or others) on the waitlist ahead of me. When I got to the airport, I was given one of the 3 J seats. So if it's any indicator, there are long waitlists for this flight!