The solution to that concern is lead time :). Provide a way to embed a QC-safe pubkey in outputs today, give wallets plenty of time to adopt it, then there will have been years and years of lead time :)

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Arbitrarily deciding when to freeze peoples’ coins against a threat that has an unknown arrival time is irresponsible. I don’t disagree with adding quantum key schemes. I disagree with freezing peoples’ coins.