You never know, but keep checking. If you see if available for redemption then you can call in and secure the upgrade.
On one of my flights it cleared right before departure:
- Waitlist Expired
- No Availability opened up (flights pretty fully)
- Checked w/ In-Town check in 6 hours to flight (No Availability)
- Upgrade Cleared 1.5 Hours to flight at HKIA - I asked again at the CX Lounge, Last J Seat on the plane. Turns out they needed more seats in PY, it's possible I could have been op-up but it seemed pretty elite heavy. I'm sure there was probably another DM on the flight that would have gotten it over me.