Forgive my hyperbole, but not many people are going to cash in x2 GUC for what is going to amount to a Z class fare when it's possible to cash them in for a J class fare last minute.

And of course it's better for us with the uberGUC, but it's a little TOO much better for us for DL's taste. If they're cashed in for x1 $15K ticket that's more value than a lot of DM's (prior to the upcoming MQD waiver change) provide to DL in a year. And I know that's not the true cost to DL, but in terms of lost revenue potential it is. DL is never going to go for what amounts to a free upgrade to J with last seat availability. The reason the GUC's now don't clear is specifically to avoid a completely sold out J cabin well in advance. They want/need those last minute seats to be available for clients that either need to change their flight at the last minute or need to purchase that last minute full J ticket due to whatever emergency. The last thing DL wants to do is tell someone willing to shell out $15K for a ticket that there's not room for them, and multiply that by 10 if the that seat went to someone with a low bucket Y ticket that they just turned certs for.

Could there be a middle ground, possibly, but by letting the GUC's go all the way to the gate, it's really pretty close to one. While not perfect, most people who fly enough to be a DM should be able to recognize when flights are the busiest and when it's likely to clear and when it isn't.