There have been rumors for a few years now that apps can go across the platform, working on both macOS and iOS. This is really not far off since developers can already use shared code to develop mobile and desktop versions of the same apps. However, a Bloomberg report points out that Apple is launching software development tools at WWDC to make it even easier.
Called project Marzipan, these tools will help developers, but typical users will not see much difference. There will still be separate Mac and IOS apps, but these apps will share some of the same items. It is likely that Apple has already used earlier versions of these tools to develop the news, stocks, voice memos and home programs, which are cross-platform.
This is related to another rumor flow that predicts that Apple can be a day-running Intel processor for Macs, and use powerful versions of the chips in IOS devices. If developers develop universal programs at that time, it can make such a transition smoother.