I agree with you...:)
I think most problem caused from changed environments.
At first, VMware moved to ESXi.
That's a compact hypervisor kernel, not a general purpose Linux kernel. The age of vSphere ESX 4.x, I saw a some difference between ESX and ESXi.
Some IB command wasn't supported in ESXi host.
vSphere VMCI feature was deprecated. I expect that will be a key point. I think RDMA support in VM environment via vmci on ESXi hypervisor.
You can find some information on google via keyword vRDMA.
Sure! There is a overhead but it is not a HPC environment. It is more fast then general purpose ethernet protocol.
VPI+EN multi function support also same.
SRIOV on virtualization environment will be a major interface for high performance vm network.