You said "By some estimates, more than 60% of the workloads are virtualized although less than 16% of the physical servers (IDC) are virtualized (running a hypervisor)."

That being said, according to Gartner, less than a third of the Linux servers in data center have been virtualized. So, there's apparently lots of untapped optimization.

Granted, the rising license fee costs of traditional virtualization solutions, such as vSphere, are likely to be a key inhibitor for some CIOs and IT managers.

In contrast, the alternatives you mentioned -- such as Red Hat Virtualization -- are a good choice for those who want to reduce their OPEX with a lower-cost open source KVM-based subscription. In fact, there are significant additional savings when combining enterprise Linux + Virtualization http://red.ht/KBgLO5

Clearly, as you say, there's also a huge advantage for those who previously deployed only VMware solutions to migrate to a multi-Hypervisor configuration. Reduced ongoing data center operating costs are just one of the very real benefits enabled by a multi-vendor coexistence strategy.