There aren't many alternatives. Unless a cataclysm makes the whole world return to the pre-internet ages, or the whole world turns into some crime-less surveillance utopia, there will always be a use for decentralized cryptocurrencies.

And the benefit of their network effect will contaminate any pocket of freedom that may form.

So, while their relevancy may fade and fluctuate, it seems inevitable that one day, there will be a gap to fill and they'll "permanently" overtake centralized forms of money.

The only positive scenario I can conjure that also sees cryptocurrencies fade in relevance would be a shift to some kind of global "additive only" economy as Mark Nadal blurrily tries to imagine[1]. That seems farther off than 50 years, and even then some parts of the economy would always be better served by traditional cryptocurrency (maybe only the parts machines are left to handle).

[1]: https://medium.com/hackernoon/wealth-a-new-era-of-economics-...