Though unconfirmed it seems that Microsoft is planning to release the next major version of Windows in November 2014. The product will not really be called Windows 9, but Windows Blue instead. Windows 8 will receive an update later this year alongside a first beta version of Windows 9 in January 2014. Details on what Windows 9 will have to offer are vague, but it will likely have improved touchscreen support.
Here's Neowin on the topic:
According to Win8China, who have provided a number of Windows leaks in the past, Microsoft are likely preparing Windows 9 for a tentative November 2014 product launch, with a beta to be available in January 2014. Now of course this is just a rumor at this stage, however a release scheduled for late 2014 does fit with what we've heard in regards to a yearly OS update cycle for Windows. Windows Blue will be an upgrade to Windows 8 that will be launched this year, while a full version upgrade will come the following year, and naturally November is the perfect time ahead of the holiday season.