Q: gif preview on iPhoto app in iOS devices?

Is the iOS10 provide the gif preview on the iPhoto app? I hope will provide this feature in future.

I'm not sure what you mean, sorry.  iPhoto has not been supported on iOS since iOS8, so it is unlikely, that it will work again on iOS 10. Or are you asking about the Photos.app on iOS devices?

You'll have to wait and see. The animated gif previews in iCloud Drive are showing as animated in iOS 10, but any animated gif I synced to Photos is liveless. But wait for the final version going public. It may still change.