Ethereum co-founder Vitalik recently stated in the podcast "Bell Curve" that what ultimately determines the success of cryptocurrencies is the practical application of the technology. If cryptocurrencies can become mainstream, or at least become a credible alternative to mainstream like Linux, that would be a success. For example, Ethereum accounts can replace social account logins, or cryptocurrencies become part of the financial system, DAOs become an alternative to businesses or non-profits, and decentralized social media or prediction markets succeed. On the contrary, if the cryptocurrency space is remembered as a dwindling band of idealists constantly shouting, or as a group of people trading digital monkeys and celebrity photos with each other, that would be a disappointing outcome.