We'll be adding a blur animation in the near future. We actually had this in beta, but it was a real gaussian blur, which isn't performant to animate (regardless of the device), so we're exploring options here.
In the meantime, you can achieve blur effects really easily by creating a blurred layer in Photoshop/Sketch/tool of your choice, and just fading it in as needed. Check out our Secret demo for an example of this, around the 19:00 mark: http://www.pixate.com/education/demos/secret-comments/
Let me know if that works for you!