Q: What features are in Server Hyper-V that aren't in Client Hyper-V?

RemoteFX capability to virtualize the GPU and pass to VMs (Client Hyper-V does have the software GPU that's part of Windows 8 and RDP).

Live Migration and Shared Nothing Live Migration of virtual machines (VMs), since moving VMs with no downtime isn't a key scenario for IT professional use. (Also Failover Clustering isn't available in client platforms, which normal Live Migration leverages (but not Shared Nothing Live Migration).)

Hyper-V Replica, which allows an offsite replica of a VM to be maintained. (It’s highly unlikely a VM running on a desktop machine needs an offsite disaster recovery capability and if it does, it shouldn’t be running on Client Hyper-V.)

SR-IOV network, which allows VMs to directly access SR-IOV capable network adapters. (No desktop machine would support SR-IOV and the zero latency network capability SR-IOV brings should not be a requirement for desktop workloads.)

Synthetic fibre channel. (Once again, desktops won't need connectivity to fibre channel.)

Network Virtualization, which allows networks to be created that are abstracted from the underlying physical network fabric. These are useful for multi-tenancy environments or multi-location infrastructures. (Not useful for desktops.)