Guys, are we looking at the wrong threat here ?
Given a quantum magic crack, however that works, and a choice between stealing a million bitcoins, or stealing a trillion dollars, which do you think most criminal masterminds would go for ?
The infrastructure for laundering that much money through all sorts of holding companies, overseas mailboxes, financial advisors, and comparable intermediaries is all well established, and when it is time to take the money and run, you can always sell CDO's of junk bonds whatever those get called next time.  So, from "what would the criminal mastermind do with the fabled quantum crack ?", it is surmised that conventional money would probably get raided before bitcoin did.
Therefore the quantum crack would be discovered doing something terrible to somebody else's money, not my bitcoins.