Have the ability to set a side some hosts that are not part of any cluster. If a cluster starts to run out of resources (or a host dies) then virtual center brings one of these hosts in and applies the profile from that cluster to this host. (Think of storage with hotspares) Once the cluster has no need for this host. Virtual center pulls this host back out of the cluster and puts this system back in the lets call it floater pool: Also VC sends the command to put the ESX host to sleep. (Talk about on demand)

Challenges that business would have to build this around:

Storage zonning and masking

Networking as far as security and location.