It's currently not possible to import (solvable) SegWit addresses (P2SH and native) using `importmulti`. I believe that's a shortcoming we should address before release.

My suggestion would be for P2WPKH (P2SH and native) to be supported without any extra arguments. This means that a P2WPKH address/script with corresponding private or public key should work. For P2SH it means checking if the supplied P2SH address perhaps matches the supplied public key or private key when converted to P2WPKH first.

To support P2WSH, I think we need an extra field "witnessScript". When supplied, it would either be required to match a P2WSH address/script directly, or if the address is P2SH, indirectly.
"3. include_watchonly (bool, optional, default=false) Also include balance in watch-only addresses (see 'importaddress')\n"
            "\nResult:\n"
            "amount              (numeric) The total amount in " + CURRENCY_UNIT + " received for this wallet.\n"
            "\nExamples:\n"
            "\nThe total amount in the wallet with 1 or more confirmations\n"
            + HelpExampleCli("getbalance", "") +
            "\nThe total amount in the wallet at least 6 blocks confirmed\n"
            + HelpExampleCli("getbalance", "\"*\" 6") +
            "\nAs a JSON-RPC call\n"
            + HelpExampleRpc("getbalance", "\"*\", 6")
        );
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK2(cs_main, pwallet->cs_wallet);
    const UniValue& dummy_value = request.params[0];
    if (!dummy_value.isNull() && dummy_value.get_str() != "*") {
        throw JSONRPCError(RPC_METHOD_DEPRECATED, "dummy first argument must be excluded or set to \"*\".");
    }
    int min_depth = 0;
    if (!request.params[1].isNull()) {
        min_depth = request.params[1].get_int();
    }
    isminefilter filter = ISMINE_SPENDABLE;
    if (!request.params[2].isNull() && request.params[2].get_bool()) {
        filter = filter | ISMINE_WATCH_ONLY;
    }
    return ValueFromAmount(pwallet->GetBalance(filter, min_depth));
}
static UniValue getunconfirmedbalance(const JSONRPCRequest &request)