I've just been making some quick video guides for users, and I thought, would it be useful to users to include the offline grading sheet download and upload into the 'upload multiple feedback files' zip package? This way a single zip with all submitted work, plus an offline grading guide could be downloaded at once, and, when complete, loaded back to Moodle in the same way. If the offline grading sheet is missing, then Moodle could just ignore it.
Perhaps a checkbox could be used to include the grading form when requesting/submitting the student submissions zip.
Just a thought.
Adam