Check into the DoE exascale studies. Moving data from RAM into the processor eats more power, and an absurd amount if it involves an off-board network. Keeping the RAM on will decrease in power drastically soon (phase-change memory with a relatively small cache), but fetching the data error-free? Painful. The voltage gaps have to keep shrinking.
This doesn't necessarily change your VM/oversubscription scenario, but it's crucial at massive scale.