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.
{
    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 || request.params.size() > 2)
        throw std::runtime_error(
            "gettransaction \"txid\" ( include_watchonly )\n"
            "\nGet detailed information about in-wallet transaction <txid>\n"
            "\nArguments:\n"
            "1. \"txid\"                  (string, required) The transaction id\n"
            "2. \"include_watchonly\"     (bool, optional, default=false) Whether to include watch-only addresses in balance calculation and details[]\n"
            "\nResult:\n"
            "{\n"
            "  \"amount\" : x.xxx,        (numeric) The transaction amount in " + CURRENCY_UNIT + "\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"
            "  \"confirmations\" : n,     (numeric) The number of confirmations\n"
            "  \"blockhash\" : \"hash\",  (string) The block hash\n"
            "  \"blockindex\" : xx,       (numeric) The index of the transaction in the block that includes it\n"
            "  \"blocktime\" : ttt,       (numeric) The time in seconds since epoch (1 Jan 1970 GMT)\n"
            "  \"txid\" : \"transactionid\",   (string) The transaction id.\n"
            "  \"time\" : ttt,            (numeric) The transaction time in seconds since epoch (1 Jan 1970 GMT)\n"
            "  \"timereceived\" : ttt,    (numeric) The time received in seconds since epoch (1 Jan 1970 GMT)\n"