Apple has notified developers that starting on April 1, all new apps submitted must support the Super Retina display of the iPhone X.
Here’s more from an email sent to developers:
Starting April 2018, all new iOS apps submitted to the App Store must be built with the iOS 11 SDK, included in Xcode 9 or later. All new apps for iPhone, including universal apps, must support the Super Retina display of iPhone X.
While this is good news for anyone with an iPhone X, Apple still isn’t requiring any app updates to support the 5.8-inch display.