I would be a little shocked (and very disappointed) if a consensus could even be achieved to invalidate keys without explicit owner consent.

Putting that aside, assuming such a consensus were possible, I don't think there will be a clear moment in time that funds move from being non-quantum vulnerable to quantum vulnerable... i.e. in either of the relevant scenarios (quantum capabilities advance slowly), funds will be slowly moving from their current state of near-zero vulnerability bit by bit in the direction of certain insecurity. Good luck forming a consensus on defining a bright line along that spectrum for what and when would constitute "sufficient vulnerability".