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.
"1. \"hexstring\"           (string, required) The hex string of the raw transaction\n"
                            "2. options                 (object, optional)\n"
                            "   {\n"
                            "     \"changeAddress\"          (string, optional, default pool address) The bitcoin address to receive the change\n"
                            "     \"changePosition\"         (numeric, optional, default random) The index of the change output\n"
                            "     \"change_type\"            (string, optional) The output type to use. Only valid if changeAddress is not specified. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\". Default is set by -changetype.\n"
                            "     \"includeWatching\"        (boolean, optional, default false) Also select inputs which are watch only\n"
                            "     \"lockUnspents\"           (boolean, optional, default false) Lock selected unspent outputs\n"
                            "     \"feeRate\"                (numeric, optional, default not set: makes wallet determine the fee) Set a specific fee rate in " + CURRENCY_UNIT + "/kB\n"
                            "     \"subtractFeeFromOutputs\" (array, optional) A json array of integers.\n"
                            "                              The fee will be equally deducted from the amount of each specified output.\n"
                            "                              The outputs are specified by their zero-based index, before any change output is added.\n"
                            "                              Those recipients will receive less bitcoins than you enter in their corresponding amount field.\n"
                            "                              If no outputs are specified here, the sender pays the fee.\n"
                            "                                  [vout_index,...]\n"
                            "     \"replaceable\"            (boolean, optional) Marks this transaction as BIP125 replaceable.\n"
                            "                              Allows this transaction to be replaced by a transaction with higher fees\n"
                            "     \"conf_target\"            (numeric, optional) Confirmation target (in blocks)\n"
                            "     \"estimate_mode\"          (string, optional, default=UNSET) The fee estimate mode, must be one of:\n"
                            "         \"UNSET\"\n"
                            "         \"ECONOMICAL\"\n"
                            "         \"CONSERVATIVE\"\n"
                            "   }\n"
                            "                         for backward compatibility: passing in a true instead of an object will result in {\"includeWatching\":true}\n"
                            "3. iswitness               (boolean, optional) Whether the transaction hex is a serialized witness transaction \n"
                            "                              If iswitness is not present, heuristic tests will be used in decoding\n"
                            "\nResult:\n"
                            "{\n"
                            "  \"hex\":       \"value\", (string)  The resulting raw transaction (hex-encoded string)\n"
                            "  \"fee\":       n,         (numeric) Fee in " + CURRENCY_UNIT + " the resulting transaction pays\n"