We have frequently been asked why we removed the option to add and remove the Server GUI package to the Windows Server 2016 Server Core install option like you could in Windows Server 2012 R2. This was one of those challenging functional trade-offs that sometimes need to be made during product development. Here is the context behind this change.
We prioritized consistency with the Windows client desktop over the ability to switch between Server Core and Server with Desktop. Replacing the legacy desktop in Server with the Windows 10 desktop experience resulted in our inability to support the Windows Server 2012 R2 behavior.
It was our belief that consistency was the top priority for Remote Desktop customers, IT Professionals accustomed to having a consistent GUI for server management, and application developers building a consistent experience between client and server.
We are working on improvements to the remote management experience to make it easier to operate and manage Server Core without the need to switch back and forth.