What needs to be realized is that a high value bitcoin will give a tremendous economic incentive to invest into mining.
At 3600 coins a day even at current prices we are looking at up to half a billion dollars a year of new value created (until halving)

Now you can fill in the blanks on how much might be spent to gain a piece of that pie.
Lets face it. If bitcoin gains global adoption mining will be a multi billion dollar industry.

Does this mean the current value is unsustainable? I really don't know.
The numbers speak for themselves. Either we will see a very big change in mining or a very big change in value.