iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Will No Longer Approve Apps Using Unique Device Identifier (UDID) Beginning May 1, Must Also Support iPhone 5 and Retina Display
Instead, Apple requests developers use the new 'Vendor or Advertising identifiers' that were introduced in iOS 6. Developers will also be required to support both the Retina display and the iPhone 5's 4-inch display, beginning on May 1.
Using Identifiers in Your AppsApple announced in 2011 that it would be phasing out developer access to UDID's, and instead create a non-identifying marker for advertisers to use. A year ago, it was reported that Apple began quietly rejecting apps for the use of the UDID, but this public announcement suggests Apple has gotten more serious about shutting down use of the identifier.
March 21, 2013
Starting May 1, the App Store will no longer accept new apps or app updates that access UDIDs. Please update your apps and servers to associate users with the Vendor or Advertising identifiers introduced in iOS 6. You can find more details in the UIDevice Class Reference.
Make Your Apps Look Great on the Retina Display and iPhone 5
March 21, 2013
Starting May 1, new apps and app updates submitted to the App Store must be built for iOS devices with Retina display and iPhone apps must also support the 4-inch display on iPhone 5. Learn about preparing your apps by reviewing the iOS Human Interface Guidelines.
Apple had been under increased pressure to change how the UDID works due to the privacy implications of a developer knowing which particular iOS device is being used to access their app. Apple and several app developers were sued over the use of the UDID to track users across different apps. While the UDID doesn't specifically identify a user, the sharing of UDIDs across ad networks and apps can help piece together a valuable picture of activity and interests of the user of a specific device. Apple seems to be requiring apps to generate their own unique identifiers for each installation to avoid this ability to share such information across apps.