It is not so much virtualisation
as it is consolidation. The old adage 'Don't keep Your Eggs in One Basket' applies very well here.
If you go Borg, then one virus in the main matrix blows it all. If you then say well I will start putting up Checkpoint Charlies then you move away from consolidation and into autonomous systems anyhow.
Virtualisation is useful for Q&A, namely Testing. But, it is not that useful in consolidation because consolidation by its own nature is a weaknesses, it is simpler to envisage but that doesn't make it better in operation.