Microsoft has been announced an update for Windows RT, 8.1 and Server 2012 R2 which is now available in TechNet and MSDN. General Public will get this by 6th April.
however it will not contain the Generic Start Menu as it will only contain in Update 2 which is not yet announced.
find here the changes contains in this package – http://blogs.windows.com/windows/b/windowsexperience/archive/2014/04/02/windows-8-1-update-important-refinements-to-the-windows-experience.aspx
This package contains 6 Separate Installer files and Here is the recommended order of installing.