So at WWDC 2016, ATS was announced as being mandatory as of January of 2017. At least for iOS.
Finding documentation about what's changing has been tricky (but I suppose I could hunt through a few WWDC videos to find the one or two slides where this is mentioned).
Will NSExceptionDomains exceptions be allowed for macOS Sierra apps? Or will my app magically stop working as of January without some server intervention?
The change is in regards to what App Review will allow into the Mac/iOS App Store (without "reasonable" justification). It is not a behavior change in the OS itself, and existing apps will continue to work.
First up, there have been no changes to the technical behaviour of ATS (other than the addition of
NSAllowsArbitraryLoadsInWebContentandNSRequiresCertificateTransparency). From a technical perspective, ATS exceptions in the newly seeded OS releases work the same way as they do in the current OS release.What has changed is that App Review will require “reasonable justification” for most ATS exceptions. The goal here is to flush out those folks who, when ATS was first released, simply turned it off globally and moved on. That will no longer be allowed.
Source: Post from Apple Developer Relations / Developer Technical Support