Well, this is something I was working on this past year on and off around that time where that one designer, Jay Machalani, caused a good stir on the interwebs with his Windows 8.2 concept. I saw faults with it and decided to make my own concept after seeing the number of faults currently with Windows 8 and its implementation. Now that rumors around Windows 9 might actually axe out the Desktop UI for smaller tablets, default the UI based on device, and potentially even switch UIs if a keyboard of a dock is connected; better now than never to show off what I was working on!
http://i.imgur.com/TYTBdHc.png (this is a pretty large image, anti-dial up)
So what we have here is not a Desktop, not the "metro UI" but the new "Workspace" of Windows.
The problem I see with Windows 8 is what many already have said, small tablets are awesome with the Modern UI but suck with the Desktop. Large monitored desktops excel at the Desktop, but get constricted with the Modern UI. 2-in-1 tablets and the Surface Pro tablets can strike a balance between the two, but not ideal you need to use two different input types and might just regress back to what's familiar to use, let alone the feeling of split UIs. Now, he thought of hard switching UIs in one version of Windows. I see problem with that because since it leaves the 2-in-1 convertibles and Surface tablets in a grey zone of, "Do I use the Desktop or do I stay with the Modern UI?" Even more problematic, say for example your fancy Surface Pro 3 with an i7 processor, 8 gigs of RAM, 512 gig SSD, and it's lovely 12 inch screen. If you had to stay with the Modern UI as that designer thought of, you will effectively underutilize your hardware as you can only physically do two apps at a time. With the Surface Pro 3, you can do four but that is kind of constricted. So your literal 2,000+ dollar tablet you thought you could rule the world with can only do two things actively at once. Lovely.
Then there's what's being rumored with Windows 9 and actually switching UIs on you depending on if you connect a keyboard. I sure hope that's not true as that in itself will cause so much confusion than need be. If you were using a Surface Pro 3 and needed to send an email to someone, you open the modern Mail app, but then click in your keyboard. Right away, it switches you to the Desktop to do so. You started with one UI, end in another. Facetious.
Any power user that has the physical space to do so adds a secondary monitor. More monitor, more windows. There's even an ultra widescreen monitor that released a few years ago that was basically two monitors fused together. More screen, more windows.
But, more windows doesn't necessarily mean more things get done.
Whoever said overlapping windows means efficient multitasking must not have been efficient nor had a Taskbar.
I define multitasking efficiency as being able to USE a window and VIEW a window.
Let's do a little experiment. Open two window panes and snap them next to each other. What you have in front of you is the most multitasking efficiency. You can both SEE those two windows and USE those two windows since they're not covered up or partially masked. You can ACTUALLY multitask. Now open a random program or a new window pane of something. That efficiency of USABILITY and VIEWABILITY is destroyed. In my case if I do this, this is almost a 40% loss of efficiency. Open another program, you might get another decrease in efficiency. Do this more and might not be able to actually find those two original snapped windows by just clicking on the header of them. This is why the Taskbar was devised because that was how Windows worked until 95 with overlapping windows getting out of hand and little way of managing them.
That's how the idea came to me. It's almost like a virtual Desktop you find in some Linux distros, it's even like a virtual monitor, and it's kind of how Windows Phone handles app switching. It flows. It can quite literally be used on ANY, literally EVERY PC regardless of input method and work just fine. It doesn't require UI switching, it scales. If you have a large monitor(s), you can even tile four window panes in one view. You move your mouse pointer, and window UI controls appear. You touch the screen for a gesture, it works just as well. It can be configured to show or hide the Taskbar on whatever edge of the screen you like. The Windows Workspaces takes on where the Desktop left off and modernizes it. It's scalable, flexible, efficient, logical, adaptive. It allows both WinRT and Win32 programs to run side by side each other seamlessly.
Of course, this is just a concept I thought of and crudely put together in Photoshop. This is just one of the main details I thought of, such as an AWESOME multimonitor setup to manage where programs on running on what monitor as well as semantic view of all open windows. I was working on a new File Explorer and have a few nifty ideas on that, but still need to actually make a mock up, stupid federal jury summons got in the way during the time I was making this.
But basically, there is life beyond the old Windows Desktop and the old WIMP window management system. What we have now with Windows doesn't work as well as it can and something better has to be thought of to make it work the best it can. I personally don't think changing UI styles is it, nor necessarily doing a Windows PC and Windows Mobile setup. I also don't believe in arbitrary software restrictions that limits the hardware, such as only two programs to be used at one time before having to constantly switch apps all the time. What I have is an idea, and I leave it at that.