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?
CKey key = DecodeSecret(strSecret);
        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();
            
            for (const auto& dest : GetAllDestinationsForKey(pubkey)) {
                pwallet->SetAddressBook(dest, strLabel, "receive");
            }
            
            if (pwallet->HaveKey(vchAddress)) {
                return NullUniValue;
            }
            
            pwallet->UpdateTimeFirstKey(1);
            pwallet->mapKeyMetadata[vchAddress].nCreateTime = 1;
            if (!pwallet->AddKeyPubKey(key, pubkey)) {
                throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
            }
            pwallet->LearnAllRelatedScripts(pubkey);
        }
    }
    if (fRescan) {
        RescanWallet(*pwallet, reserver);
    }
    return NullUniValue;
}
UniValue abortrescan(const JSONRPCRequest& request)