Blockchain-based currencies are not exactly in danger of quantum encryption cracking, but I can see a lot of hard-forks happening though. There are quantum resistant encryption algorithms, Post-quantum cryptography - Wikipedia.
Does anyone know of any crypto-currency toying with quantum-attack resistant algorithms? I wonder...
I guess it makes sense since the blockchain is an open public ledger there is nothing to hide from the quantum computer. Maybe the quantum computer would be helpful to break the code for the bank's data instead.