Like the iMac?
There are lots of ways they could be creative and make it work. As the "iDevices" get more powerful, "iOS" can become a GUI for OS X. It's pretty sad that in its current state OS X can't run smoothly on top end hardware. Apple needs to clean out the crud. It should be an embarrassment that, in contrast, Windows will run on practically anything. Anyway, the iPad "Pro" (ugh) could load a desktop when docked or when keyboard attached but the "iOS" GUI when in tablet mode. There really is no reason people can't have both. And if OS X were to be optimized accordingly, it would absolutely fly on full size laptop and desktop hardware.
I realize the implications of different processor architecture, but that's where the Apple creativity and ingenuity comes in. I think they can do a better Surface giving Apple users what they are used to getting plus some new Jobs-free flexibility. There is something to be said for simplicity but it can be the user's choice. Do folks realize that Windows can be dead simple? It runs things like ATMs that perform a very simple singular function and no one sees the Windows running things behind the scenes. OS X can be made more modular and users can be given the choice of what they want and don't want in their desktop and touch interfaces.