Reply to comment:

Bill Owens
I've seen a couple of people confused about the changes that Apple has made with iOS 9 and IPv6, including this article. There are two things being conflated: iOS 9 has changed the algorithm for choosing between v4 and v6 from treating both equally to providing a small preference for v6, and at some point in the future the App Store will require IPv6 support for all apps so that iOS 9 devices will be capable of working in IPv6-only environments. The preference change should drive more IPv6 traffic, and early results indicate that this is happening. The details of the App Store change are apparently still being worked out, with Apple saying only that the requirement will go into effect "starting in early 2016."