Illustrative systems and methods enable a virtual machine (“VM”) to be powered up at any hypervisor regardless of hypervisor type, based on live-mounting VM data that was originally backed up into a hypervisor-independent format by a block-level backup operation. Afterwards, the backed up VM executes anywhere anytime without needing to find a hypervisor that is the same as or compatible with the original source VM's hypervisor. The backed up VM payload data is rendered portable to any virtualized platform. Thus, a VM can be powered up at one or more test stations, data center or cloud recovery environments, and/or backup appliances, without the prior-art limitations of finding a same/compatible hypervisor for accessing and using backed up VM data. An illustrative media agent maintains cache storage that acts as a way station for data blocks retrieved from an original backup copy, and stores data blocks written by the live-mounted VM.