Virtualization: CPU and memory hotplug

Linux kernel supports cpu-hotplug mechanism. You can enable or disable CPU without a system reboot. CPU hotplug is not just useful to replace defective components it can also be applied in other contexts to increase the productivity of a system. For example on a single system running multiple Linux partitions, as the workloads change it would be extremely useful to be able to move CPUs from one partition to the next as required without rebooting or interrupting the workloads.

Is this feature useful in a Virtualization setting?   Should KVM support CPU and memory hotplug?    Are there some customer who say, well, doesn't matter if this feature exists, I don't trust hotplug, I will restart my VMs to ensure data integrity?

I need your help to figure out the timing for supporting this, RHEL7 timeframe or earlier?