As of iOS 6 beta 3, when you start a coordinated read operation on a file or package for which you already have a local version, the coordinated read will be granted as soon as possible, and the new version, if any, will download in the background.
On previous iOS releases, when your app performed a coordinated read operation on a file or package and the iCloud daemon noticed that there was a newer version of the item available, the coordinated read operation blocked until the newer version of the item was downloaded and written to the disk.