[benjaminjackman]

It's definitely a possibility (not sure how likely though).

"In the comments section of the Antonoupolos’s talk, reddit user @cfromknecht explains that there are flaws to the Elliptic Curve Digital Signature Algorithm (ECDSA), and it is very possible that quantum computers will be able to work faster than the transactions, therefore beating the encryption. “Whenever you spend bitcoins, you must include a signature that approves the spend, which is done using ECDSA” they explain, “If these signatures can be broken faster than transactions can be confirmed, an attacker could sign a different transaction that spends your coins before the original transaction is ever accepted.”

https://edgylabs.com/quantum-computing-hacking-blockchain