We recently reported that many Apple retail stores are running low on stocks of AirPort devices, and this is usually a strong indicator of an upcoming product refresh. 9to5 Mac has followed up on that and says its sources claim a refresh is indeed imminent. A new version of the Time Capsule, currently undergoing internal testing at Apple, will cache software updates for any devices that regularly connect to its Wi-Fi network. The device will "learn" which devices regularly connect to it and silently download updates for them in the background without user intervention.
This functionality will work for both Macs and iOS devices, enabling users to install software updates from local caches instead of waiting for them to download first. John Gruber of Daring Fireball also speculates this could enable devices such as the iPad and iPhone to perform software updates without being tethered to a Mac, as is currently required.
9to5 Mac points out this technology already exists in Mac OS X Server, although in a more simplistic form that downloads software updates of all types rather than device-specific varieties. They also speculate that these new Time Capsules could be tied into iCloud, caching music in a user's online storage locker or large, frequently accessed files, and also providing user backups to iCloud.
No one knows for certain when such devices will debut, nor can we say with any certainty that they even exist. All we know thus far is that current stocks of AirPort devices are dwindling at some Apple stores, and while WWDC is expected to focus on software, that doesn't specifically preclude the introduction of new hardware like a Time Capsule update.