Microsoft can't just do a u-turn and go back to the traditional desktop. What they need to do is to scrap the old desktop altogether and use the screen real estate that's there.
Why not implement a fully featured tiling window manager? On a small screen, you see only one or two tiles and you have no discoverability. On a larger screen you get extra tiles that show available commands and help text. Once you learned your shortcuts you can remove those tiles.
* contextual menus should still be available to speed up certain tasks. For touch screens these should be available through a simple gesture, for mouse/keyboard it's the right click as always. I'm thinking that for touch UI the menu entries could be placed in a circle around the point where the gesture has been initiated, without hiding anything behind the finger (the OS should recognize from what direction the finger has been placed on the screen).
* the concept of a program menu should be reimplemented. Every function should be accessible through this menu, even if there are contextual elements that implement them as well. However, this menu needs to be easily usable on touch screens as well.
* there's one element I'd propose to be always visible, no matter what screen size starting at 7 inch: The search. This search should be able to find application commands and data, OS commands, other applications as well as and system wide data (in that order).
You can't even hover a mouse cursor over something you suspect might be a control because there is no mouse cursor and what is and isn't a control isn't always clear either. Lots of secret gestures and lots of change in every version (at least on Android).
I'm a bit baffled as well as to why this can work. I suspect it might be because people don't use these devices for productivity and hence they only use a relatively small number of features. They don't need to discover new stuff all the time and when they do it's for entertainment more than anything.
Or maybe it's because there's a new generation of mainstream users that sees everything as a kind of adventure game where discovering hard to find treasures is the whole point.
Maybe Microsoft's problem is that their technology people ignore the very message their marketing people are trying to get across: PCs are for productivity, for creating things. If you're at work trying to get things done you're not in the mood for figuring out obscure features and the latest UX fashions.