well I wouldn't say it is threatening Iceland's power supply since Iceland basically has unlimited free power (geothermal mostly), but the general point definitely holds that a real issue with bitcoin is the ridiculous (and growing) electricity costs necessary to mine. One of many reasons I don't see Bitcoin sticking around for very long, or at least, not sticking around and being relevant. it is already almost irrelevant, the transaction "speed" and fees are so ridiculous that the idea of using bitcoin as a payment network is pretty much already relegated to fringe cases/large transfers. I seriously doubt Bitcoin will still have the largest coin market cap by end of 2018.