Serialized array, grab specific posts with meta_key/meta_value[0]->is_featured

It is possible if you shape your meta query to look for the serialized string like this, assuming your array value is always an integer:

$params = array(
    'meta_query' => array(
        array(
            'key'     => 'mediSHOP_product_extras',
            'value'   => 's:11:"is_featured";i:1;',
            'compare' => 'LIKE'
        )
    )
);
$query = new \WP_Query( $params );

If the array value is a string or a boolean, the meta query value pattern should be altered:

// for string type values
's:11:"is_featured";s:1:"1";'

// for bool type values
's:11:"is_featured";b:1;'