In addition to deprecating OpenGL support and adding a revamped App Store for MacOS, Apple confirmed today at its WWDC event that it's been working to update its UIKit framework to work well on MacOS.
The big takeaway here is that sometime next year the company plans to make their work broadly available to devs, potentially making it easier to port UIKit-reliant iOS and tvOS games to MacOS.
According to The Verge, versions of Apple's own iOS apps (e.g. News and Stocks) were shown running on the new version of MacOS (10.14, aka "Mojave") during the WWDC keynote, utilizing elements of UIKit that have been integrated into Mojave.
While UIKit apps running on MacOS seem capable of playing nicely with common desktop computing behaviors like resizing windows or dragging and dropping files, Apple was reportedly adamant that it is not unifying iOS and MacOS. To keep tabs on this initiative, bookmark Apple's UIKit dev documentation.