Re: OS !== UX && OS !== CPU
Linux runs Android and can run desktops. So a common kernel is already a reality…
That's a bit sweeping and, as a result, misleading. The monolithic Linux kernel does support lots of different archs but tends to get customised for each one as a result. Then there is the boon and curse of the different layers, especially when it comes to GUIs which is why both Android and MacOS (some fanboi has just edited one of my questions on AskDifferent to use the "official" writing) mandate their own tightly coupled app frameworks and why lots of people moan about Android not being a full Linux.
With the Mach kernel Apple should have it easier porting the majority of the OS services to different archs and it has been doing for years on simplifying the GUI toolset. Though it probably wants to refactor some of the IOS settings that have grown all kinds of warts in the last few years.
But a toolkit that works for both a touch and mouse interface is notoriously difficult to get right. As always the devil is in the detail of the kind of widgets you want in which environment. I'm seeing this with the Gemini, which is a lovely device (sound on mine could be unusually poor), that is at the limits of a keyboard and touchscreen interface (you can reach the lower part of the screen with your fingers while typing) where a lot of widgets are being caught out on the half-height screen. But you can do a lot and for the rest you can let developers provide different settings information for different widgets for different resolutions. Developers will appreciate this if it is done correctly and one of the reasons for the popularity of QT's QML, I believe.
As for converged devices, I'll believe them when I see them. Apple might well let others test the water and make a splash when it thinks there is a market to be had (it stopped pioneering years ago).