As you know Windows Server 2012 Essentials is primarily designed for small businesses that need support for up to 25 user accounts and up to 50 devices. But even beyond this, Windows Server 2012 Essentials provides a number of unique, value-added features, such as Remote Web Access and automatic client computer backup, which many customers and partners want to have available in larger environments.
As in my previous session on “What do you do with Windows Server 2012 Essentials when you grow beyond the 25 user ceiling?” , here is another scenario which is new for Windows Server 2012 Essentials, but has been available in the Windows Server family for some time. The downgrade rights for Windows Server 2012 Standard and Datacenter have been expanded to include the Windows Server 2012 Essentials edition. This means that when you purchase, or receive as a Software Assurance (SA) grant, a Windows Server 2012 Standard license, you can choose to run Essentials as one of your two virtual instances, without having to purchase Essentials separately.
Remember that Windows Server 2012 Standard allows you the virtual use rights for up to 2 virtual instances, which means that you can install Windows Server 2012 Essentials on one of those instances and use the other for an application virtualisation workload or a line of business application.
This right is documented in the Windows Server 2012 Licensing FAQ as well as in the latest Microsoft Product List and this downgrade right is available to all customers in all available channels (except for SPLA), including volume licensing (VL), OEM, and retail (FPP).
"Q15. If I want to use the bits from an earlier version or edition, what are my options?"
Remember that the ability to run downgrade bits does not change the licensing or support terms in which you can use the product you purchased, for example if you purchase Windows Server 2012 Standard, you will need Windows Server 2012 CALs even if you choose to downgrade an instance to run Windows Server 2012 Essentials.
If you purchase an OEM or retail copy of Windows Server 2012 Standard, you can download Windows Server 2012 Essentials and obtain a product key to use during installation from the TechNet Eval Center, and then perform an in-place license transition by using your Standard product key, which gives you a fully licensed and supported instance.