I don't think if you said to him "Hey, we can create new quantum resistant address types on the existing chain through a soft fork" he would be opposed to that. I think he would prefer that. But I believe his point still stands, everyone would have to move their coins to the new addresses. The old addresses would be drained. I don't think it is possible to just upgrade without moving your coins to a different address, either on the same chain or a different one. Am I wrong here?