Cryptocurrencies are a customer serivce battle between the government and the banks. So ultimately, the cryptocurrencies that will be sustainable will focus and execute on two things:
1 Easy end user experience. From aquisition to wallet safety
2 Community engagement. This means multiple things but primarily, a) where can people actually use the currency b) What inspires people to switch from fiat to cryptos from a practical purpose.
In 2018, most people in the crypto space are speculators. They don't care about practical uses for cryptos. They care abot ROI. Until you get past those people, into legit problem solving / pain points, cryptocurrencies are just a mechanism for semi/legal gambling.
This is not to say that cryptos aren't important. Last year there were about 1600 of them. As of June 2018 there are roughly 4000 ICOs/cryptos being planned. Do we need that many currencies? No. But cryptocurrencies are a blockchain awareness, education and adoption campaign. And that is worthy of a tip of the hat. Because the tech, blockchain, is where the future is at. Most likely a tokenized furutre. So its not that cryptos aren't important but most will be non-exchange traded tokens in the future.
In summary, we'll have less than a dozen cryptocurrencies in a decade. While nearly every business will have a token. Led first by Bank of America (as they already have a non-crypto-coin), Amazon and then the other banks masquerading as fintech companies: Alibaba, Apple, Uber, etc... The future will be tokenized, as a reward for customer loyalty. Imagine being able to share airline points and exchange flight tickets, as easily as sending a text message. Thats tokenization at work. And thats the future.