It seems that there are hints of a fourth-generation Time Capsule and fifth-generation AirPort Extreme, at least according to sleuths who have pored over the most recent source code for an AirPort security update.
The code references caching were extremely specific, where it allows the aforementioned rumored devices to be able to download software updates in the background, followed by waiting for some user input before said updates will be applied. Definitely far more useful than having you to manually download the update yourself, no? What do you think? Do you forsee us getting new Time Capsure and AirPort Extreme models soon?