If you did not see this announcement from Somasegar, check it out! You can now download release candidate of Visual Studio 2013 and RTM! version of Windows 8.1. This means that you can start moving your existing 8.0 apps to 8.1 if you would like. There is also a slew of cool new features you can read about in the same blog post. This means Microsoft reversed its previous decision to make Windows 8.1 available to MSDN subscribers in October. Good for them and for us, developers!
Enjoy.