Most probably Bitcoin will be the only and most PoW blockchain but it does not mean Bitcoin will continue to dominant the market. there will be game changer blockchains, which are more efficient, scalable, flexible and utility in more than one aspect(which is only payment system). imagine a blockchain which provide finance functionality(not only transaction but loan & lending...) also a bunch of functionality based on blockchain promises, which today each startup(aside shitcoin inventors) tries to implement an small part of it. this blockchain(or better naming blockgraph) is coming in the picture as the need of that emerged.