I Have tried the Views Data Export module to export orders from a Drupal Commerce Kickstart installation. But the line items gets rendered as an html-table.
I am not sure if this is possible with the Views Export module, but I want to loop through each line item to achieve something like this:
<order ordernr="1">
<customer_profile id="1">
...
</customer_profile>
<line_items>
<line_item sku="786">
<price>100</price>
</line_item>
etc...
</line_items>
</order>