The new `getrpcinfo` shows a list of the active commands and the duration each command has been running. This sounds like a good place to report a completion percentage for any command doing a blockchain rescan, to solve [this problem](https://bitcoin.stackexchange.com/q/83236/90721).
"  \"details\" : [\n"
            "    {\n"
            "      \"address\" : \"address\",          (string) The bitcoin address involved in the transaction\n"
            "      \"category\" :                      (string) The transaction category.\n"
            "                   \"send\"                  Transactions sent.\n"
            "                   \"receive\"               Non-coinbase transactions received.\n"
            "                   \"generate\"              Coinbase transactions received with more than 100 confirmations.\n"
            "                   \"immature\"              Coinbase transactions received with 100 or fewer confirmations.\n"
            "                   \"orphan\"                Orphaned coinbase transactions received.\n"
            "      \"amount\" : x.xxx,                 (numeric) The amount in " + CURRENCY_UNIT + "\n"
            "      \"label\" : \"label\",              (string) A comment for the address/transaction, if any\n"
            "      \"vout\" : n,                       (numeric) the vout value\n"
            "      \"fee\": x.xxx,                     (numeric) The amount of the fee in " + CURRENCY_UNIT + ". This is negative and only available for the \n"
            "                                           'send' category of transactions.\n"
            "      \"abandoned\": xxx                  (bool) 'true' if the transaction has been abandoned (inputs are respendable). Only available for the \n"
            "                                           'send' category of transactions.\n"
            "    }\n"
            "    ,...\n"
            "  ],\n"
            "  \"hex\" : \"data\"         (string) Raw data for transaction\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
            + HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\" true")
            + HelpExampleRpc("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
                },
            }.ToString());