I'm sure the world banking system's going to raise a defence against quantum hackers before they're able to attack & break encryptions. They're working with the best devs today to avoid getting hacked. If quantum hackers break military encryptions we're in trouble.
Why wouldn't the ppl with quantum tech make bitcoins their first target to exploit. They're hackers so they'll follow the roads which takes them to where there's money. I can't think of any bigger targets which quantum hackers want to steal more than bitcoin.
For a start, targets such as the worlds banking systems and any other financial ones are far bigger targets.