WinBeta claims Microsoft's next operating system will include an updated version of the Modern UI when it launches in 2015. Metro 2.0 is expected to feature a bunch of new functionality to align it with competing tablet operating systems like iOS and Android.
The new Modern UI is exclusively for tablets whereas laptops and desktop computers will get the traditional desktop interface. Unlike Windows 8.x, there will be no middle ground of devices that have both the Modern UI and the desktop, with Windows 9 you cannot have both.
The removal of the desktop has been talked about about in the past, and will be mostly apparent with Windows RT devices. Current Win32 applications are being replaced with Modern UI alternatives which means the desktop will have no real use. Of course, the removal of the desktop isn't for all devices, so don't be alarmed fellow desktop users.
The idea with Threshold on tablets is to make it an immersive experience. The inclusion of the Desktop with Windows RT was a huge mistake for Microsoft. It's a jarring transition between both environments and consumers never really knew which one they wanted to use. With Threshold, Microsoft wants to make sure that devices which run the Modern UI and devices which run the desktop and distinctly different, and the way they're doing this is simple.