No sci-fi writer predicted bitcoin mining. The rulebook vaguely stated that a cyberpunk knows a few unlawful ways to get money, so should a game such as Cyberpunk 2077 include a subplot based on simply publishing images bugged with Monero-generating code (to use just one recent example)?
Also, a friend of mine has an idea that the first true unkillable AI will run inside a blockchain, and it would be economically infeasible to hack it as it would require owning more than 50% of its infrastructure. But that's still sci-fi.
Diamond age had a distributed tuple space, which was kind of similar in effect, enclaves that made their living off of work their computers did for digital pay.
Of course, the standout thing about cryptocoin by comparison is that there's no real useful work resulting from all the absurd amounts of electricity being used to mine it.
They have some utility, if you're willing to ignore the majority use case (get-rich-quick schemes), but ultimately, they're like decorating by hanging pictures on quadcopters instead of nailing them to the wall. The pictures are technically hanged, but it's kind of a dumb use of energy.
Maybe blockchain technologies go the way of the car phone. That is, they were novel and useful for a time but other advancements rendered them obsolete. Or, maybe future fiction doesn't need to account for every possible future technology and instead will feature fictional things/ideas the author simply thinks is cool/interesting to play with.
Also, a friend of mine has an idea that the first true unkillable AI will run inside a blockchain, and it would be economically infeasible to hack it as it would require owning more than 50% of its infrastructure. But that's still sci-fi.