Hi
I think, try with:
$node.object.data_map.message.content.output.output_text
or
$node.object.data_map.message.content.output.output_xml (I'm don't remember)
Use {attribute_view_gui attribute=$node.object.data_map.message} or take a look at the code used in design/standard/templates/content/datatype/view/ezxmltext.tpl.