I recently opened a new PR to allow migrating fewer posts at a time (such as testing one at a time) and added tests for the task.
It feels like it makes sense to start with posts, since you want to rebake posts to change the URL in the cooked post after each migration; migrating all the uploads and then starting the rebakes would leave the site very broken for potentially a long time for a large site (I need to migrate about 100GB from S3 to local, so I care). But what I wrote might help start writing a migrate_uploads_from_s3 task that would be run after migrate_from_s3 in order to clean up uploads that weren’t part of posts.
@zogstrip What’s the current status of “We’re working on…” — is this still in flux or is this migration now worth paying attention to?