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?
pwallet->MarkDirty();
                if (!pwallet->AddWatchOnly(pubKeyScript, timestamp)) {
                    throw JSONRPCError(RPC_WALLET_ERROR, "Error adding address to wallet");
                }
                
                if (IsValidDestination(pubkey_dest)) {
                    pwallet->SetAddressBook(pubkey_dest, label, "receive");
                }
                
                CScript scriptRawPubKey = GetScriptForRawPubKey(pubKey);
                if (::IsMine(*pwallet, scriptRawPubKey) == ISMINE_SPENDABLE) {
                    throw JSONRPCError(RPC_WALLET_ERROR, "The wallet already contains the private key for this address or script");
                }
                pwallet->MarkDirty();
                if (!pwallet->AddWatchOnly(scriptRawPubKey, timestamp)) {
                    throw JSONRPCError(RPC_WALLET_ERROR, "Error adding address to wallet");
                }
                success = true;
            }
            
            if (keys.size()) {
                const std::string& strPrivkey = keys[0].get_str();
                
                CKey key = DecodeSecret(strPrivkey);
                if (!key.IsValid()) {
                    throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key encoding");
                }
                CPubKey pubKey = key.GetPubKey();
                assert(key.VerifyPubKey(pubKey));
                CTxDestination pubkey_dest = pubKey.GetID();