Windows Phone 8.1 for the general public (not the developer preview that has been available) could hit the market as soon as next week with the launch of the Nokia Lumia 630. A release in China could come at any time. The Windows Phone 8.1 update could start rolling out late next month, obviously, considering the date when Microsoft will start supporting it.
Meanwhile, for you poor souls still stuck with a Windows Phone 7.8 model, Microsoft's support of the build expires on September 9th. It might be time for you to start scouting out your next handset.
Microsoft will support Windows Phone 8.1 from June 24th, 2014 through July 11th, 2017; support for Windows Phone 7.8 is about to end in just four months
source: Microsoft via WMPoweruser