Quantum computers are threat to Bitcoin?
What to do if Bitcoin's cryptography seemed like it would be broken in a few years because of quantum computers?
Some people said we should upgrade to a quantum proof encryption algorithm but do nothing else, and once the crypto eventually gets broken, anyone with money in non-quantum proof addresses will simply have it stolen, leaving potentially millions of bitcoin in the hands of one thief.
Theymos argued that this would be a systemic risk to Bitcoin, and it would be better to give people a few years to send coins to a quantum proof address, and then freeze all unprotected coins assuming they were lost. From the victims perspective this is about the same as having the coins stolen, but it would be far safer for the ecosystem as a whole.