The ERC-4337 standard basically solves quantum attack problems

If everyone moves to smart contract accounts with arbitrary transaction signing mechanisms, then you can easily use a quantum safe scheme.

Only vulnerable actors will be the people running bundlers, but consider they also have their own smart contract accounts and only keep small balances on the EOA.

Then if a quantum computer appears and starts hacking the chain, only these bundlers will be affected, and only a small part of their funds. And when that happens (if ever) we can start worrying about forking the chain to implement quantum safety in the protocol.