Reorganize category hierarchy plugin

Hello all,

Does anyone know of a plugin for easily reorganizing category hierarchies?

I have recently been using Drupal which in contrast to its general interface failings has a very nice javascript category management system (categories in Drupal speak are vocabulary and terms). A user can drag a term (category) and place it anywhere along the vocabulary tree, and indeed nest terms. The changed order is then saved when the user clicks the save button. This beats WordPress’ edit an individual category parent select box.

I am currently working on a site with 160 categories all at the top level(!). They are in desperate need of (re)organizing, as currently the categories are fulfilling the IA functionality of WordPress tags even though these are themselves very well utilized. To organize and maintain the categories individually is going to be a nightmare. A bonus to this project is the post permalink URLs are not based on categories, so any changes won’t affect the SEO.

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For any developers out there: is there a programmatical reason such a plugin may not have been created? I can hazard a guess that the relationship between posts, categories and sub-categories, and permalinks might be quite complicated.

Thanks!