featured doesnt exist or isnt featured
$meta_query = array( 'relation' => 'OR', array( 'key' => 'featured', 'value' => '1', 'compare' => '!=', ), array( 'key' => 'featured', 'compare' => 'NOT EXISTS', ), );
$meta_query = array( 'relation' => 'OR', array( 'key' => 'featured', 'value' => '1', 'compare' => '!=', ), array( 'key' => 'featured', 'compare' => 'NOT EXISTS', ), );