I definitely think that proof-of-work is going to be phased out soon, though proof-of-stake isn't much better, they all require specialist hardware in order to run their networks, which is not something we should implement for later generation blockchains, a waste of energy can't be the best way to secure a blockchain. I notice that the major blockchains are starting to shift towards POS as it's definitely more environmentally friendly than POW, but it also increases centralization and the risk of a vector based attack so we should look for even better alternatives in future.