Great plugin! Only a couple of suggestions that I think could improve it.
- Activate/deactivate reordering for specific post types (posts, pages, and each custom post type) from an Options screen. Sometimes you don't want end users to be reordering pages.
- Allow to filter posts/pages/CPTs by related taxonomies or published status before reordering. I ran into a couple of cases where I had to show all posts sorted alphabetically in one section, but only the posts tagged under a specific category sorted manually in another.
Thanks for the effort, and feel free to ask if you need any help.