476 votesEsben Barnkob commented
The datacenter license is likely already purchased since your cluster contains or will contain, so many VMs that you need the datacenter license anyway. Also the datacenter license can be transferred from your previous virtualization platform if covered by SA.
People need to compare this to VMware vCloud Suite + VSAN Enterprise + Microsoft CIS Datacenter, and suddenly the "Datacenter licensing requirement" is no longer crazy. Actually there is a great business case for dropping 2/3 of the licenses of VMware, which amounts to about 2/3 the cost of the virtualization layer.