Here’s an open source component allowing you to apply motion blur to your animations using a custom Core Image filter created using the Core Image Kernel Language (available with iOS 8) from Arkadiusz Holko.
The blur is pre-calculated so the performance is extremely high (except on the Simulator because the GPU is used), and Arkadiusz has written a nice writeup explaining the techniques he used to apply the motion blur to animations – the creation of the filter is explained in WWDC 2014 sessions 514 and 515.
Here’s an animation from the readme showing the motion blur effect in action:
You can find the MotionBlur component on Github here.
You can find the Arkadiusz’s guide explaining how the filter is applied to animations on the Holko blog.
If you’d like to watch the WWDC lecture about the advanced Core Image techniques used to create this motion blur filter you can find it on the Apple developer site here in the videos entitled "Advances in Core Image" and "Developing Core Image Filters In iOS".