Windows 8 failed because it tried to merge desktop and tablet UI paradigms.
Switching between entirely different and separate "UI personalities" could work.
I don't think the pointer vs touch UI is the main thing that people have in mind when wishing for macOS on the iPad though, instead a "proper" UNIX-style filesystem and shell, and the ability to install any software outside the app store via a package manager and without Apple's nanny reflex getting in the way.
So you're saying my Steam Deck, which has both a "game console" UI and a desktop UI mode and lets you switch between them, is somehow running two OSes? Weird argument.
Switching between entirely different and separate "UI personalities" could work.
I don't think the pointer vs touch UI is the main thing that people have in mind when wishing for macOS on the iPad though, instead a "proper" UNIX-style filesystem and shell, and the ability to install any software outside the app store via a package manager and without Apple's nanny reflex getting in the way.