Is this what Microsoft is going with for a logo? We can't be sure, but it came from them.
It appears that Windows 9 is indeed going to be the next major OS from Microsoft if the above image, posted by Microsoft China has anything to say about it.
The Verge reports that Microsoft China, through it's Weibo account, posted a teaser today asking "Microsoft’s latest OS Windows 9 is coming soon, do you think the start menu at the left bottom will make a come back?" with the above image accompanying the post.
Chinese site Cnbeta was able to grab the image and post details before it was pulled shortly after. Clearly a mistake by the Chinese Microsoft division, but the wording suggests Windows 9 is indeed "coming soon."
Although we can't be sure the Windows 9 logo image is official, the "9" made up of tiles does seem to tie in with the Modern UI philosophy, and is possibly a shout out to multiple desktops finally coming to the OS.
Microsoft is expected to announce the Technical Preview of Windows Threshold on September 30th, and then, or shortly after it will be made available to the public.
Windows Threshold (or Windows 9) will see the return of the Start menu after its brief hiatus from Windows 8, and is expected to include windowed Modern apps as well as an overhaul of the Modern UI, currently known as Modern UI 2.0, that will make it more desktop friendly.
For more details and frequently asked questions on Windows Threshold, take a look at our "Answers to the questions you've been asking" article.
[Update] The image released by the Chinese arm of Microsoft is a wallpaper from a few months back made by a fan and is not an official image With that being said, this is still an official Microsoft channel talking about Windows 9 which is a first for the company.