Rather than being a sweeping overhaul in the vein of Windows 8, Windows Threshold actually appears poised to dial back the gargantuan changes found in that operating system. Microsoft has already announced that the Start menu is coming back to the OS, joined by the ability to run Metro apps in discrete desktop windows. Recent leaks (including Foley and Warren's own reports) suggest other, mostly pro-desktop tweaks are inbound, including virtual desktop support, the removal of the Charms bar, and—possibly—the introduction of Windows Phone 8.1's sassy virtual assistant, Cortana, to Windows proper.
Hopefully there's more to Threshold than simple UI changes. We can think of other features we'd like to see in Windows 9—15 of them, in fact. We'll know for sure what's making the cut before long, if the two reports prove true. And if they do, Microsoft will reportedly make the technical preview public, so that developers and enthusiasts alike will be able to take Windows 9 for a whirl. Fingers crossed.
Source: http://www.pcworld.com/article/2466558/windows-9-inbound-microsoft-to-unveil-windows-threshold-in-september-reports-say.html