While I agree that the days where you should be installing a dozen NICs in your servers are behind us, I don’t think that’s solely because 10GB Ethernet has removed most of the bandwidth constraints we used to face.
Sure it’s a big part of it, but that separation is still important for security (e.g., management traffic) and Quality of Service; we’re just now able to do it with less physical NICs through the use of I/O virtualization (e.g. Cisco’s Palo CNA).
More now than ever we need to be able to leverage WFQ and other technologies to ensure a bunch of vMotions can’t clobber our Unified Communications traffic and/or that someone can’t compromise Fault Tolerance or critical management traffic and bring down our virtualized tier-1 applications.
As I understand it most of the EVB/802.1QBG/etc. technologies revolve around the problem with VLANs in large datacenters/service providers – namely they run out of them and even if they don’t, stretching them across every switch in the DC is a disaster waiting to happen (hairpins/traffic trombones anyone?).