A note (https://developer.apple.com/news/?id=09102019a) on the Apple Developer web page says that starting in April 2020, all new apps and app updates will need to be built with the iOS 13 SDK and support the all-screen design of the iPhone XS Max or later.
Apple also touts the features of iOS 13. To wit: “With iOS 13, your app can take advantage of Dark Mode, a dramatic new look for iPhone, Sign in with Apple, the fast, easy way to sign in to apps, and the latest advances in ARKit 3, Core ML 3, and Siri. Build your apps using Xcode 11 GM seed, test them on iOS devices running the latest GM seeds, and submit them for review.