Apple has posted an update to developers of iOS that requires them to use the iOS 11 SDK and to support the display of the iPhone X. The policy change goes into effect in July and any apps submitted or app updates submitted must comply with the new policy or they will be rejected.
The requirement for using the iOS 11 SDK is not a surprise. It has been available since September of last year and Apple likes to make sure that apps, just like iPhones and iPads, are up-to-date. Part of that SDK is supporting the Super Retina Display of the iPhone X, including its notch. That is now required too.
There are still a lot of apps in the App Store that do not support the iPhone X’s notch, leaving a black band at the top of the display instead of “wrapping” around it. It works but doesn’t look that great (although some would argue it does as it “hides” the notch). Starting in July, that won’t be allowed any more. Developers will have to design their apps to work natively with the iPhone X’s display.
While the announcement makes it clear what will happen to submissions starting in July, there is no mention of existing apps that are in the store already. Likely those apps will be left there (in other words, not removed) but if the developer wants to update, they have to do it in the iOS 11 SDK.