In the log I see things like:

    2017-09-13 03:54:33 init message: Rescanning...
    2017-09-13 03:54:33 Rescanning last 68616 blocks (from block 416339)...
    2017-09-13 03:54:40 AddToWallet xxxxx  update
    2017-09-13 03:55:33 Still rescanning. At block 418849. Progress=0.549138

I would be interested to see the wallet file name on each of these log lines.

Would there be any interest in merging such a PR?
throw JSONRPCError(RPC_WALLET_ERROR, "Error adding address to wallet");
            }
            
            if (IsValidDestination(dest)) {
                pwallet->SetAddressBook(dest, label, "receive");
            }
            
            if (keys.size()) {
                for (size_t i = 0; i < keys.size(); i++) {
                    const std::string& privkey = keys[i].get_str();
                    CKey key = DecodeSecret(privkey);
                    if (!key.IsValid()) {
                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key encoding");
                    }
                    CPubKey pubkey = key.GetPubKey();
                    assert(key.VerifyPubKey(pubkey));
                    CKeyID vchAddress = pubkey.GetID();
                    pwallet->MarkDirty();
                    pwallet->SetAddressBook(vchAddress, label, "receive");
                    if (pwallet->HaveKey(vchAddress)) {
                        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Already have this key");
                    }
                    pwallet->mapKeyMetadata[vchAddress].nCreateTime = timestamp;
                    if (!pwallet->AddKeyPubKey(key, pubkey)) {
                        throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
                    }
                    pwallet->UpdateTimeFirstKey(timestamp);
                }
            }
            success = true;