also I think (fairly new thought) that HD keys that were reused could be soft-forked to require a Zero Knowledge proof of knowledge of the chain code and master even if the coin private key was public information. (and soft-fork made not be spendable with direct ECDSA.).
I wonder how something like this could work considering the fact that any information provided based on hashes that could reproduce the keys could be duplicated by the other parties that are trying to steal the same coins.
That is the purpose of ZKP, isn't it? You provide a proof that you know some information without actually revealing it (and so nobody can duplicate it if you are the only one who knows the hash).