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?
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() != 1)
        throw std::runtime_error(
            "dumpprivkey \"address\"\n"
            "\nReveals the private key corresponding to 'address'.\n"
            "Then the importprivkey can be used with this output\n"
            "\nArguments:\n"
            "1. \"address\"   (string, required) The bitcoin address for the private key\n"
            "\nResult:\n"
            "\"key\"                (string) The private key\n"
            "\nExamples:\n"
            + HelpExampleCli("dumpprivkey", "\"myaddress\"")
            + HelpExampleCli("importprivkey", "\"mykey\"")
            + HelpExampleRpc("dumpprivkey", "\"myaddress\"")
        );
    LOCK2(cs_main, pwallet->cs_wallet);
    EnsureWalletIsUnlocked(pwallet);