There is a huge buzz about the new IBM zEnterprise Mainframe and its x86 Intel Based Blade Center extension called zBX. The Hypervisor for the x86 Platform is based on Linux-KVM. So theoretically, It would be possible to run Microsoft Windows Guest on this Hyper-visor as long as the drivers are supported..
There seems to be some progress on the Windows Drivers for Linux-KVM. http://www.linux-kvm.com/content/tip-how-setup-windows-guest-paravirtual-network-drivers
“Windows is not supported on zBX.” I think I would read this as, the driver are not supported yet. It would be impossible to run Windows Guest on the zEnterprise..
My two cents, It would have been better if IBM selected Xen as the Hypervisor, as Citrix XenServer is based on this and it has more mature suport for Windows and its Opensource like Linux-KVM.