Imho what they need is more integration with the Desktop, not less.
What is the point? Most users would be fine with RT as long as there is a sane version of the office pack, a good email application, etc.
For serious users, well there would still be "vanilla windows". Windows RT is API agnostic, there could be real cheap all in one pc, etc.
The desktop is the alpha and omega for serious users, I don't see how their new approach can result in something more convenient.
Desktop can be improved that is for sure but I don't think the start screen is an improvement.
So could be the start screen (some more information akin to "beautiful systray could come handy, the lack of clock is bothering too).
Not too mention that they are splitting their users bases, de facto the devs that choose to develop "apps" pass on vanilla windows user base (now they can reach xb1 and phone). They are stuck in the middle and it is not clear to their business partners (from IHV to software developers) what environment to target.
I mod my wife and my phone (Android) with Launcher 7 and 8 (2 custom UI for Android), we are both liking it, it is imo neat, close to my favorite out of vanilla Android, iOS, even plain desktop for light uses.
Since 8.1 I try to use the desktop as few as possible, and it works. If I had a "libre office App" and games I would could mostly never use the desktop (outside of really productivity work). It would need little tweak, for example when you want to switch between apps (the good old alt+tab works though) and call the charm bar, it is uselessly long aka first appears the last apps you used and then you have the list by going down, if you were getting the list directly switching between apps would be every bit as fast on the desktop.
Desktop legitimacy is for high productivity work, it could be improve with more "desktops" as on Linux, may be some configurable charms bar could be great, etc. But touch friendly (and imho light usage friendly too) UI has another purpose fulfil the modern use of computing device.