Upgrade time is going to come down in my opinion. The bypass percentage is going to only go up with the etops bid group being in the two junior bases. That and a 5 year hiring slump that is just getting ready to hit the upgrade point means it should trend down pretty significantly.
Zap is right, though, about a couple of things.
One, hiring has been at a breakneck pace while everyone else has slowed down. At some point, we will slow down too.
Two, the early NG retirements are going to happen. Management can use that to keep aircraft count (and capacity) relatively flat. In fact, for every 700 they retire, CASM goes down since all the new deliveries minus the few max 7s are all 175 seat planes.
Three, the economy is showing cracks. We will hit a slowdown at some point.