A few days ago, Priotr tried to run a management command to export all courses. When he ran into an exception, he wrote a shell script to export each course individually. When he did that, he found a bunch of courses wouldn't export.
There are a bunch of things that course authors can do that would make their course unexportable, and it seems like this is something that we'd want to guard against.
Here are some bugs that I've tagged with an export label (there may be more, but I've only recently started tagging such bugs). They're usually caused by course teams writing invalid XML in problems. I don't know if that can be solved by linting course-authored XML before saving, or if we should just export the bad xml.
We should also do discovery in categorizing all the ways in which export can fail, and look at how we can use this information to make the site more robust with export.
I'm sure and will want to chime in.