Well, in 2011, Apple removed the "Mac" in OS X, then in 2016, changed "OS X" to "macOS". So, a change 5-7 years down the road to their operating system software is not out of the realm of possibility. There's plenty of opportunity for changes to happen between now and 2025-2027. Those years are a long way away, and we all know how Apple doesn't remain static for long.They literally *just* split out iPadOS and tvOS, and they've repeatedly and consistently made it clear that while the underpinnings are shared, each platform is distinct enough that it is a separate thing.
The software in the theoretical appleOS will be intended to support all hardware platforms, but each platform would still preserve their own unique support and OS respect...ie, Watch would keep their UI compact like now, while the Mac would run appleOS like a traditional Macintosh operating system, with the menu bar, mouse pointer, etc. (assuming no major UI changes are made in a future version of macOS). appleOS would/should be scaleable to "fit" each platform, while maintaining a single OS.
IMHO, we're seeing the signs of integration slowly but surely, with AS for all devices, Catalyst applications, the UI of all OSes slowly becoming coherent, as well as the system language (just look at how similar Big Sur's Setup Assistant is to the iOS Setup Assistant; they even share similar wording). Now, look at SL and iOS in 2011; they were completely different, with very different UI's and language/naming conventions. Mac OS X 10.6.8 bore almost no resemblance to iOS 4 at the time. They were completely different OSes on the surface level; only sharing the core kernel and other similarities.
Apple will continue the slow march towards unification as the years come, IMHO, on the Mac and mobile platforms.
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