Apple quietly announced on Wednesday that developers' cross-platform apps can soon be enabled for universal purchases, which is a fancy way of saying that you - the consumer - will be able to buy an app once and use it across your iPhone, iPad, Apple TV, and Mac.
Starting this March, developers will be able to turn on this option in their app. If they do so, for the first time, those of you who buy a Mac App Store version of an app will also get it on your iOS devices (and vice versa). The idea is developers can use this feature to lure customers to buy their Mac or iOS apps. They’ll also be able to seamlessly sync in-app purchases and subscriptions across platforms.
"Starting in March 2020, you’ll be able to distribute iOS, iPadOS, macOS, and tvOS versions of your app as a universal purchase, allowing customers to enjoy your app and in‑app purchases across platforms by purchasing only once. You can choose to create a new app for these platforms using a single app record in App Store Connect or add platforms to your existing app record. Get started by building and testing your apps using a single bundle ID with Xcode 11.4 beta. In addition, categories will be unified across the App Store and Mac App Store to align with this change, and to help make your apps more discoverable."
This new feature for developers is likely part of Apple’s push to get developers to create more Catalyst apps - ie Apple's attempt at making it easier for developers to port their iOS apps across to the Mac.