Mulling this, I am quite confident that a practical post-quantum ZK proof emergency salvage system could be designed not based on seed derivations, but for all UTXOs that require unrevealed public keys. This includes P2SH/P2WSH. The only coins that could not be safely salvaged are those in addresses with known public keys: Reused P2PKH/P2WPKH, all P2TR, reused P2SH/P2WSH multisig, etc. (About those, I absolutely agree with you that coins vulnerable to theft cannot be locked or seized; the idea flies in the face of all that Bitcoin means!)
But what about all those other UTXOs (reused P2PKH/P2WPKH, P2TR, reused P2SH/P2WSH multisig)? I think that is the main dilemma here. I would quote Pieter Wuille here:
"If a QC can ever spend lost ECC-locked coins, I believe it's game over for Bitcoin. How can an asset maintain value if an attacker has the ability to flood the market with the significant portion of the entire supply?".
I don't like the idea of some coins being locked by consensus, however, Pieter has a point that the economical impact of flooding the market with all these coins could be unsurvivable.