StarWind is not a VSA on a Hyper-V. It does not run inside guest virtual machine rather it runs directly on top of a hypervisor turning DAS into high performance and fault tolerant SAN.
So it's already possible for more then a 2 years to do with Hyper-V what's still in beta with vSphere 
Basically VMware team is on the right track with the product: VM-running storage definitely has issues
(guest VM overhead, NFS overhead as block level storage is always faster, scalability etc) and a) running on a hypervisor b) SAN rather then NAS are both a way to go.
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Do you have any documentation/blog post supporting that statement that hyperV already has a VSA? Or are you referring to other vendors providing this capability to hyper-V (eg Starwind)