I would like to be able to update the categories of a number of assets at the same time.
Consider a document folder with 20+ documents, I want to be able to select say 8 of them and then apply a set of category and tags to those 8, replacing any tags they may have had before or adding the ones I select to them if they didn't have them before.
Web content is another asset type this could be useful on.
The Control Panel UI allows you to select the objects so shouldn't be too hard to develop a new action method to handle this.
