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?
"1. \"filename\"    (string, required) The filename with path (either absolute or relative to bitcoind)\n"
            "\nResult:\n"
            "{                           (json object)\n"
            "  \"filename\" : {        (string) The filename with full absolute path\n"
            "}\n"
            "\nExamples:\n"
            + HelpExampleCli("dumpwallet", "\"test\"")
            + HelpExampleRpc("dumpwallet", "\"test\"")
        );
    LOCK2(cs_main, pwallet->cs_wallet);
    EnsureWalletIsUnlocked(pwallet);
    boost::filesystem::path filepath = request.params[0].get_str();
    filepath = boost::filesystem::absolute(filepath);
    /* Prevent arbitrary files from being overwritten. There have been reports
     * that users have overwritten wallet files this way:
     * https://github.com/bitcoin/bitcoin/issues/9934
     * It may also avoid other security issues.
     */
    if (boost::filesystem::exists(filepath)) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, filepath.string() + " already exists. If you are sure this is what you want, move it out of the way first");
    }
    std::ofstream file;
    file.open(filepath.string().c_str());
    if (!file.is_open())
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot open wallet dump file");
    std::map<CTxDestination, int64_t> mapKeyBirth;
    const std::map<CKeyID, int64_t>& mapKeyPool = pwallet->GetAllReserveKeys();
    pwallet->GetKeyBirthTimes(mapKeyBirth);
    std::set<CScriptID> scripts = pwallet->GetCScripts();