I really don’t see this working, not because iOS has some nice UI cues, but because iOS is designed for no more than a few apps running at any one time. Even worse, the ‘screens’ approach means these apps interact in a very clunky and linear way. Okay if you are working between two apps, you can run split screen, but what if you want to do something else? The conceptual problems with iOS are the very things OSX solved: multitasking between loads of apps at the same time and managing their windows. Likewise menu bar apps offer another layer of always available apps and toggles. The ability to drag and drop objects everywhere creates a powerful and fast working environment – one not matched on iOS that requires combinations of presses and touches (which reminds me of right-clicking on windows). Cut and past on macOS is way more convenient, particularly using a keyboard.
I’m going to push the boat out here and propose the opposite thesis. With faster hardware and more memory how does iOS become as flexible and productive as macOS?
I’d suggest as Microsoft has tried the uneasy hybrid approach and Apple doggedly sticks to strict separation, no one has yet solved this problem. The field is wide open. Whether the conceptual UI problems can be solved or if a leapfrog interface evolves is open to debate.