I think it's likely that proof of work algorithms will be obsolete as PoS and DPoS become more mature.  All of the unnecessary electric consumption with PoW mining is obviously not good.  However the real issue with Bitcoin or any other PoW system are the fees.  Even with the upgrade to the lightning network there will still be fees on the network.  Steemit is a DPoS which internalizes the cost of running the network to the witnesses.  Witnesses are incentivised with block rewards.  This allows the users to use the platform freely and it also pushes the theoretical transactions per second to 100,000+.  There are flaws to PoS and DPoS which will be exploited in the future.  It will be a learning process but they will become more balanced and secure as these issues are identified.