Great Plugin. I suggest a few improvements.

Great plugin to add a functionality that should be already in wordpress core. I have a few improvements to suggest:

– option to show all terms visible in a simple list, without the need to click the arrow to hide/show their children terms. Preferably without javascript, thus making it easier to style the list with custom CSS only.
– option to make the initial state of the children lists all expanded instead of hidden.
– option to hide a parent term but not their children.
– option to make a parent unclickable, working only as a visual parent for their indented children list.
– different sorting options other than alphabetical.
– add a class to terms that are associated with current post so it can be highlighted with CSS.
– advanced mode where user can select multiple terms before submit, working as a search filter, and a button for clearing all selected terms.