Just another data point...
My wife and I are headed SFO-ORD on Saturday and when I looked earlier this week, only five seats showed free on the seatmap in C, so I figured our UDUs wouldn't clear and we'd have to see what happened at the gate.
Much to my surprise, about 50 hours out I received an EasyUpdate text that the UGs had cleared.
Logged into .bomb to choose seats and saw the dreaded Upgrade: Denied, but also saw that our seat assignments were now N/A and there was no listing for our confirmed Y segment. Went through seat selection, which let me choose seats in C, and followed up with a call to 1K reservations. The CSR said she saw us as upgraded and didn't know what the "Denied" meant.
In contrast, our return on Monday passed the upgrade window today and now shows Denied, but .bomb still shows us confirmed in Y, so I'm guessing we're still waitlisted.