The File/Export/Plain Text (Taskpaper) function is very welcome but does have one obvious bug:

It fails to export the "completed" / "done" status of actions (this should be represented in Taskpaper format with an end of line tag " @done")

At present completed items are exported with their context tags, and the "done" status gets dropped.

If the concern is to preserve context information, then the obvious approach would be to have both a context tag and a "done" tag.

e.g.

- Pay electricity bill @home @done

Taskpaper has no problem interpreting lines like this.