I'd like to restrict the tags that users can view, add, and edit in the admin panel.
Any chance you'll implement this feature or build a separate plugin for it? I would certainly donate some money.
I know there is an old thread which asks about the same thing but the mentioned plugin does only restrict which tags can be used in edit mode. http://wordpress.org/support/topic/plugin-restrict-categories-restrict-categories-and-tags?replies=6