It's rumored that it will be possible to run Metro apps in windows on the desktop, and that Microsoft may bring back the Start menu as an option:
Metro apps running in windows on the desktop. As you can today with third-party utilities such as ModernMix, the next version of Windows will let users optionally run Metro apps in floating windows on the desktop.
Start menu. After bringing back the Start button in Windows 8.1, Microsoft will take the next logical step in the next Windows version and make the Start menu available as an option. It's possible this will appear only on those product versions that support the desktop.