A few lines in a recent Airport software update point to new 5th generation Apple Time Capsule and Airport Extreme models that could include a software update caching feature that will grab updates for all of your hardware on the network and then serve them up to various computers on the network. It’s a wildly boring feature, to be sure, but it will speed up software updates and, more important, reduce the amount of bandwidth Apple has to blow out at any one time when it releases a update.
The code has appeared a few times in previous versions of the software so there’s no telling whether the new hardware will have this feature. However, it’s clear Apple is currently testing the new feature on current or future hardware.