The implementation of the additional tags is very helpful - thanks !

The remaining problem is that task/sub-task hierarchies are still being flattened by the exporter.

To conform to the Taskpaper format, and to achieve round-tripping with my stopgap Taskpaper to Omnifocus import droplet, sub-tasks need to be tab-indented.

For comparison, try exporting from nested Omnifocus tasks both with the export routine that you have in version 96487, and with my export script.