Today Skype has received an update for iOS 8 to v5.5. Now Skype takes advantage of the new features introduced by iOS 8. Rich lock screen and heads up notifications are now a part of the Skype app on iPhone.
When you receive a Skype call you can press voice or video to jump into the call. Also if you are using your iPhone and get a message, a notification will appear at the top of the screen. By tapping reply you can reply the the message right away without leaving your current app and going to the Skype app.
Rich notifications are a feature of iOS 8 which is why it was so easy for Skype to implement these changes. These types of notifications were leaked with the original images of Windows Phone 8.1, but were pulled before launch. Hopefully interactive notifications will be coming to Windows phone soon.