I see several things wrong with this pov. First, stop assuming they're Satoshi's. We don't know that. Second, when/if they are spent, we won't know how the private key was known to the spender. Quantum's existence won't change that epistemic limitation. Third, there is no "we" to make such a choice. No group of people have the right to confiscate coins, no matter how rational the reason.
And to *anyone* (not Matt specifically) who is worried about the market effect of huge selling, consider the market effect of the precedent of freezing coins at the protocol layer. Everything is a one-time exception until it isn't.
Notice that that last point is not wrong because "if QC then all btc is worthless"; we are discussing the scenario of there being a migration path but old plain pubkey holders don't use it