To take into account of new iOS 8 and Yosemite features including app extensions, HealthKit, HomeKit and TestFlight, Apple has this week updated their App Store Review Guidelines for developers. The bulk of the new features are covered in the new guidelines in sections 25 to 28.
Furthermore, Apple has slightly changed one of its introduction dot-points to specifically warn developers not to create "plain creepy" apps.
We have over a million Apps in the App Store. If your App doesn't do something useful, unique or provide some form of lasting entertainment, or if your app is plain creepy, it may not be accepted.