The only existential threat to #Bitcoin that I’ve been able to come up with is a zero-day fast crack of ECDSA signatures. If this happened, then there may not be time to soft-fork in a quantum-resistant signature scheme. Pirates would be able to spend a great deal of the existing coin, violating the “your keys, your coins” sacred rule.

A slow crack of ECDSA is more likely, where it’s possible but extremely costly (and slow) at first, but then speeds up over time. In this scenario, we’d expect to see Satoshi’s stash start to move first, since these are the largest bounties. That would be the bellwether signaling that we should soft-fork in an alternative signature scheme and start to migrate coins over.