I'm going back to previous posts to see what plugin features could be implemented, and I haven't answered this one. I believe that should already be possible using the data API, by setting the order property of the note. Then you could create two commands that grabs the currently selected note and move it up or down.
And finally you would associate these commands with menu items, which will allow you to se a keyboard shortcut. If you decide to give it a try and need some info, let me know.