The requirements that need to be met are as follows:
• Guest OS in the VM supports remote desktop services (e.g., Windows 8.1 Pro/Enterprise/Windows Server 2012 R2)
• The server policy in Hyper-V Manager server settings for Enhanced Session Mode is enabled (Enhanced Session Mode Policy, Allow enhanced session mode.) It's disabled by default.
• Remote Desktop Services service is running in the guest (but the Allow remote connections to this computer in System configuration doesn't need to be enabled).
• User logging on is as a member of local administrators or remote desktop users in the guest.
• Out Of Box Experience (OOBE) has been completed.