The next major version of Windows is expected for spring 2015, with possibly a beta release next fall. While Microsoft might propose a new update for Windows 8.1 in the month of August, the new features would be with Windows Threshold (code name for the next version of Windows).
Microsoft seems to want to make Threshold the version that Windows 8 should have been. Struggling to democratize in the universe of the desktop PC, Windows 8 is not a commercial success for this segment.
With Threshold, the operating system would be different depending on the device on which it is installed. Desktop PCs would benefit from an accessible desktop directly with various improvements and a true menu start. This famous menu start also was seen during the alpha Build 14 version. Also, the Modern UI of Windows 8 start screen may disappear completely.
On hybrid devices such as the Microsoft Surface or the Yoga of Lenovo: it's the presence or not of the detachable keyboard that would activate the desktop mode or the Modern UI interface. Finally, with mobile devices, the Metro environment would be the only option as it is currently the case.
Microsoft is reportedly considering to offer Windows Threshold for free users of Windows 8.1.
We will see in spring 2014 if these rumors of the "back to the roots" of Microsoft will be true or not.