"Of course they have to be confiscated. If and when (and that's a big if) the existence of a cryptography-breaking QC becomes a credible threat, the Bitcoin ecosystem has no other option than softforking out the ability to spend from signature schemes (including ECDSA and BIP340) that are vulnerable to QCs. The alternative is that millions of BTC become vulnerable to theft; I cannot see how the currency can maintain any value at all in such a setting. And this affects everyone; even those which diligently moved their coins to PQC-protected schemes."