But in this context, I merely asking. How fast can the Core Developers react IF an actual Quantum Computer is projected start breaking SHA-256 in one year?
Questions like this don't make sense. Core developers are not the ones developing quantum resistant hashes and encryption, they are doing the implementing. If there is a need, an implementation can be delivered fast. That is not a concern.
Anyhow, the chance of SHA-256 being broken within this century is close to 0%. Why worry about such nonsense, you won't be alive to see it?