I don't believe the power consumption is unsustainable when compared to global power consumption, as using that metric its nill. I do; however, think that power consumption is unsustainable in terms of cost/benefit from the perspective of the ever shrinking group of consolidated miners. In the comments of the first article I posted you will find discussion on that front, as well I summarized it here:

https://steemit.com/bitcoin/@pawsdog/need-mathematical-help-mining-costs