14 DAY TRIAL // Apple really wants developers to have their apps ready for the latest iOS 8 Beta and OS X Developer Preview. An email sent today by the Apple Developer Technical Support Team explains the most recent for CloudKit features.
Apple representatives say CloudKit, iCloud Drive, iCloud Photo Library, Mail Drop, Safari History, and Call History will require iOS 8 beta 5, or OS X Yosemite Developer Preview 5 or later. This is a change that applies to all developers building apps that use these features and services.
In other words, this is Apple's way of pushing the developers to have their apps compatible with iOS 8 and OS X Yosemite as soon as the new updates come out. Also, as 9to5Mac notes, this may be due to an older sandbox server being taken offline as the operating systems comes closer to reaching their public releases.
CloudKit is dubbed to be the simplest way for developers to store stuff and provide authentication for their users. Apple offers a free tier for app data storage with a pretty high limit so most of the developers can benefit of that and they can forget about buying expensive servers.