syrwhizzy,
I can understand your frustration.
I recently flew to SYD RT on Delta in BE and thought my data point might help. I was able to get a BE seat under the "book a higher class economy fare (M+) and upgrade to BE for 1 mile" promotion. I believe this is essentially the same thing as a PMU or upgrading with miles.
I was able to lock in BE on my outbound flight (July 25) but nothing was available on my return leg (Aug 30). So they put me on the wait list. A few weeks later, they cleared me for the Aug 30 flight in BE. I then changed my return date to Sept 5 and wasn't able to get confirmed until a few days before the flight. I had to switch my return flight again last minute to Sept 6 and there were upgrades available at the last minute.
What I have learned from this:
- Delta holds off until the last few days to release the Z seats. I called numerous times inquiring about the return flight and there were almost always BE seats available for upgrade within a few days out. Anything beyond that... forget it! Although if I waited a few days and called again, those flights that were a week away now all of a sudden had BE seats available. Tracking some of the flights, it looked like there were usually ~20+ open seats in BE from SYD to LAX. When I ended up taking my return flight there were still a handful that were empty from SYD to LAX.
So I would say you have a good shot at getting the BE upgrade but just not until a few days within the actual flight. This is unfortunate though as it requires you to buy the higher class fare without having the guaranteed upgrade at the time of booking (which no one likes doing).