According to a post from Brad Anderson the release date for several products will all be the same: 18 October 2013.
These are of course Windows Server 2012 R2, Windows 8.1, SYstem Center 2012 R2 as main components.
Because these products were developed together and work together to form a number of great new scnearios these are also now release together and will work together as well.
Here is the post from Brad:
http://blogs.technet.com/b/in_the_cloud/archive/2013/08/14/mark-your-calendars-for-oct-18-the-r2-wave-is-coming.aspx
So lets get ready for this!
Bob