Apple plans to combine apps made for iPhone, iPad and MacOS by 2021. Bloomberg reports that Apple will allow developers to create a single app, known as single binary, that will work over iPhone, iPads and Macer. Apple already revealed part of this work, codenamed marzipan, last year at the company's Worldwide Developer Conference. Apple has started bringing iOS versions of Home, Stocks, News and Voice Memo apps to macOS 10.14 Mojave.
A combined universal app is obviously a much larger step, and Bloomberg reports that Apple will manage this in stages. Developers are said to be able to send their iPad apps to Mac later this year, thanks to a new SDK, and this will be extended to iPhone apps by 2020 to bring them to MacOS. SDK is rumored to be unveiled at this year's WWDC.
Apple's plans are very similar to Microsoft's own efforts with its Universal Windows Platform. Microsoft had pushed the idea of a single universal application for Windows phones, tablets and PCs. Microsoft gave up its Windows Phone efforts in 201
Microsoft's universal applications still exist, but the software giant has pushed developers to bring their desktop applications to the Microsoft Store instead of creating a single app spanning devices such as Xbox One, HoloLens, PCs and tablets.
Apple has not yet released its WWDC 2019 dates yet MacRumors recently uncovered the potential dates of 3-7. June. Apple is also expected to uncover its plans for iOS 13 at WWDC, including a dark mode and new iPad home screen. Bloomberg also notes that Apple has "internal weighted preview" a new Mac Pro at this year's WWDC.