At this point, I would think that the limitation will be how many pilots can be trained. They're buying simulator time just to try to increase output.
I'll be surprised if they opted to shut down training this summer - they need as many pilots as possible to fly as many aircraft as possible because there is strong passenger demand. Coupled with very low fuel prices, a lot of flying that was previously a money loser should now be profitable.

With rumors of United scouring the world for used aircraft, it looks like they're trying to add as much capacity as possible right now. More capacity is needed. Load factors are in the low/mid 80s so capacity is pretty much maxed out.