Multi object editing - UV_OT_export_layout (80%).
I saw UV_OT_export_layout mentioned in an email with a subject of 'Blender 2.8 Python Meeting Notes', I'm not up to date with what that really means so I'm stopping any more work on this and adding a diff of what's been done so far.
Apart from the 'export as PNG' all seems to be working ok (as seen with my inexperienced eyes).
'Export to PNG' also seems to work but doesn't look acceptable because the mesh wireframe modifier is used to draw UV wireframes (I was going to see if a curve object would be usable to draw wireframes). Something in setting the renderer up could also be wrong or missing.