Some comments from @sipa in #12702.

___

Yes, I think `importmulti` is superior in every way, except:
* Slightly less convenient to use (it requires redundant information, as you have to explicitly state what you want to import, and then give the keys/... to enable that).
* ~Doesn't support P2SH-P2WPKH yet~. Added in #14454

The latter can be fixed by just adding support for that case. The former can be improved by adding 'default' cases (e.g. if you prove a WIF private key, it can permit omitting the address, ...).

{
    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() > 2) {
        throw std::runtime_error(
            "sethdseed ( \"newkeypool\" \"seed\" )\n"
            "\nSet or generate a new HD wallet seed. Non-HD wallets will not be upgraded to being a HD wallet. Wallets that are already\n"
            "HD will have a new HD seed set so that new keys added to the keypool will be derived from this new seed.\n"
            "\nNote that you will need to MAKE A NEW BACKUP of your wallet after setting the HD wallet seed.\n"
            + HelpRequiringPassphrase(pwallet) +
            "\nArguments:\n"
            "1. \"newkeypool\"         (boolean, optional, default=true) Whether to flush old unused addresses, including change addresses, from the keypool and regenerate it.\n"
            "                             If true, the next address from getnewaddress and change address from getrawchangeaddress will be from this new seed.\n"
            "                             If false, addresses (including change addresses if the wallet already had HD Chain Split enabled) from the existing\n"
            "                             keypool will be used until it has been depleted.\n"
            "2. \"seed\"               (string, optional) The WIF private key to use as the new HD seed; if not provided a random seed will be used.\n"
            "                             The seed value can be retrieved using the dumpwallet command. It is the private key marked hdseed=1\n"
            "\nExamples:\n"
            + HelpExampleCli("sethdseed", "")
            + HelpExampleCli("sethdseed", "false")
            + HelpExampleCli("sethdseed", "true \"wifkey\"")
            + HelpExampleRpc("sethdseed", "true, \"wifkey\"")
            );
    }
    if (IsInitialBlockDownload()) {