You forgot Satoshi's 1000000 bitcoins that have newer been moved, but still have their public keys visible.
Those addresses are difficult to protect from QC, because even if we implement a QC-resistant algorithm, those can't be protected or otherwise even Satoshi couldn't move them.
Actually once you soft fork to add the quantum resistant code, you might also add something to keep those coins locked forever. Something along the lines of: By the date the new code activates, coins not moved to a new wallet that supports it become locked.
we've had these discussions before and the consensus (i think) is that it's not ethical to steal/lock satoshi's coins. bitcoin users never opted into a rule system where their outputs would be forcibly locked after a certain time. i understand the motives to do it but a fork like that would definitely split the network. it's too politically contentious. it would be a different story if the protocol were designed that way from the start.
i'm sure we'll eventually fork to a quantum resistant signature scheme but the fork won't do anything to stop vulnerable coins from being spent. those coins will eventually be stolen over time.