I would assume that creating temporary tables is possible even if the user lacks the permissions to create (permanent) tables:

CREATE GLOBAL TEMPORARY TABLE my_temp_table
        (...)
      ON COMMIT DELETE ROWS;
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As to the larger issue, I think it's mainly an issue of the DBD to return the structured data from the XML query, and maybe supporting that isn't that easy without the driver becoming "locked" to a specific version of Oracle.