As a twist on this, the VMware paravirt driver interface is soAny hardware engineer (myself included) will tell you that, generally
hardware-like that they're getting hardware vendors to supply cards that
implement it. Try that with a pure software approach.
speaking, what you can do in hardware you can do in software (think of
what QEMU does today, for instance). It's purely a cost/performance
tradeoff.
I can at least tell you that is true of vbus. Anything on the vbus side
would be equally eligible for a hardware implementation, though there is
not reason to do this today since we have equivalent functionality in
baremetal already.
The only motiviation is if you wanted to preserve
ABI etc, which is what vmware is presumably after. However, I am not
advocating this as necessary at this juncture.