There’s an updated (Dec 2014) Volume Licensing Brief for licensing Windows for use with virtual machines. The main changes, as you would expect, are for Windows per User licensing and all of the scenarios are updated which means, of course, that the Companion Subscription Licence is banished to obscurity. Get the document here: http://bit.ly/IKPKXE.
Windows Companion Subscription Licences will have the same use rights as if they were Windows Enterprise SA per User Add-on USLs, starting on 1 December 2014.
See page 77 of the October 2014 Product Use Rights document.