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?
file << strprintf(" # addr=%s\n", address);
        }
    }
    file << "\n";
    file << "# End of dump\n";
    file.close();
    UniValue reply(UniValue::VOBJ);
    reply.pushKV("filename", filepath.string());
    return reply;
}
static UniValue ProcessImport(CWallet * const pwallet, const UniValue& data, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(pwallet->cs_wallet)
{
    try {
        bool success = false;
        
        const UniValue& scriptPubKey = data["scriptPubKey"];
        
        if (!(scriptPubKey.getType() == UniValue::VOBJ && scriptPubKey.exists("address")) && !(scriptPubKey.getType() == UniValue::VSTR)) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid scriptPubKey");
        }
        
        const std::string& strRedeemScript = data.exists("redeemscript") ? data["redeemscript"].get_str() : "";
        const UniValue& pubKeys = data.exists("pubkeys") ? data["pubkeys"].get_array() : UniValue();
        const UniValue& keys = data.exists("keys") ? data["keys"].get_array() : UniValue();
        const bool internal = data.exists("internal") ? data["internal"].get_bool() : false;
        const bool watchOnly = data.exists("watchonly") ? data["watchonly"].get_bool() : false;
        const std::string& label = data.exists("label") && !internal ? data["label"].get_str() : "";
        bool isScript = scriptPubKey.getType() == UniValue::VSTR;
        bool isP2SH = strRedeemScript.length() > 0;
        const std::string& output = isScript ? scriptPubKey.get_str() : scriptPubKey["address"].get_str();