To which I say:  It really doesn't matter so long as everyone is playing on a level field.  If someone comes up with a 100TH machine that runs a 1000W (~10X todays performance) at the same price point as todays solutions, the world will simply convert to that technology and difficulty will rise 10X.  Power consumption would remain the same.  All of todays tech would simply become land-fill.

The only benefit would be to the first adopters (who will likely pay a capital premium), and that disappears once everyone is using the tech.

The the primary two constraints are Power availability and resulting Heat generation, I highly suspect packaging would be developed that mimics todays machines - drawing around 1400 watts and simply providing 10X the hashrate.    Personnally, I would be swapping those in one-for-one for my existing gear - no energy savings at all in terms of actual usage.