If you apply for the upgrade prior to May 25th, and there is availability for award seats in U class, you will be confirmed. This is for flight before and after May 25th. However, if there is no availability in U class, then you will have to join the upgrade waitlist. If the waitlist clears before May 25th (ie U availability is reviewed and becomes available), you will be confirmed for the upgrade.
If the waitlist has not cleared before May 25th, you will remain on the waitlist and confirmation will not be forthcoming until Check-in. I am assuming this will then work like the current domestic on-Departure Upgrades (ODU), where any unsold seats can be made available for upgrades, and not just U class availability. But we will need to wait and see just how that affects upgrade availability.
With the sharp increase in poits needed for upgrades after May 25th, and the steady decline in upgrade credit availability, we may find there are less people seeking upgrades (people can't affort them). We may also find that the U seat allocation for the flight is not taken by upgrades meaning more award flights will be available for people.
So as much as I don't like the idea of not having an upgrade confirmed in the weeks/days before travel, I have not yet drawn a conclusion about the good/bad sides of this policy change. As a Platinum FF member, it may well mean better chance of an upgrade (all unsold seats are now in the upgrade pool vs U class seats). It also gives even more incentive to ensure I continue to requalify my Platinum status.
