By 2020 BTC will consume the same amount of energy as all the world together today, this is not just a high cost problem but makes BTC a very dirty technology and problem for our environment. The environmental damage because of it will be much greater that what BTC problem intent to solve, will PoW be the en of BTC?
That's why ethereum will be migrating into the pos system as fast as possible. How so many people are using a lot of energy to secure the bitcoin network and make it still decentralized. I think that there will be a lot of the new coin that will be used environmentally friendly energy. Pow is really bad imo.