The universal apps would be presented in 2019 and the first would arrive in 2020/21
At this point, few people who follow the world of Apple may be surprised that universal apps are being talked about among iOS and macOS. It is a rumor that has been around for a long time and, it seems, this year it would be confirmed.
Universal apps would be presented at WWDC 2019 and would start appearing in 2020 or 2021
The universal apps project was called the Marzipan project. On many occasions rumor mills have focused on this project and Mark Gurman, one of the great "rumorologists" in the Apple world, has focused on it again.
As indicated, we would see the first phase of that project this year. Specifically at WWDC in June where Apple would show the Development Kit for developers. This would be the Kit that would allow the creation of universal apps for iOS and macOS.
An application that gives access to the Mac. iOS and macOS together
The presentation of the kit would be in June of this year, but its launch would not be. Some developers will likely have access to it before anyone else, but for developers in general the kit would be released in 2020. From then on, we might start to see universal apps.
What Apple is looking for with this movement is, without a doubt, that the Mac App Store looks empowered. In the App Store of iOS there are many applications and, in fact, the developers prefer it to other application stores of other operating systems.
For Mac, the Mac App Store although it has a good number of applications, it is somewhat more limited. In this way and with the new universal applications, it would be as simple as requesting the upload of the iOS application to the macOS app store so that the application would be present on both iPhone as in Mac
We'll see how this project progresses. We will have to wait to see its presentation in June and if the reception by the developers is good.