Microsoft is currently working on two different Windows projects, both of which are supposed to bring major improvements to the otherwise disappointing Windows 8 released in October 2012.
It appears that Microsoft has worked out a much more complex long-term plan for its Windows platform, as the company might actually delay Windows 9 in case Windows 8.1 fails to excite, just like the operating system it's based on.
According to some new rumors, Microsoft is also pondering the release of a second Windows 8 upgrade, possibly called Windows 8.2, which could bring a number of improvements to Windows 8.1 and likely to be unveiled in 2014.
If this is true, launching Windows 9 during the same year won't make much sense, so Microsoft would basically have no other choice than to delay the next full Windows release.
Of course, you shouldn't take this for granted, but don't be too surprised if Microsoft decides to continue the Windows 8 upgrade frenzy next year.