Q: Will I be able to push the Windows 8.1 upgrade to my organization by using Windows Server Update Services (WSUS)?
A. No. WSUS is a great capability to allow the deployment of patches to machines using an internal source instead of Microsoft update servers on the Internet; however, Windows 8.1 isn't a patch or service pack, but rather a new version of the OS.
This means it needs to be deployed by using normal OS deployment mechanisms, such as System Center Configuration Manager, or executed from a share (Volume Licensed), or, for OEM/retail machines, via the Windows Store.