In addition to having folders and files within dropbox having some kind of icon indicating they have tags associated with them, another key feature would be to have a centralized tag directory or "pool" that could allow users to not only view all active or inactive tag, but also delete and add en masse tags to files and/or folders as well.
The line of work I deal with as a Global Asset Coordinator is that I am building out and organizing our assets in various ways and levels. Automation tools have been a help, but to truly achieve maximum efficiency and ease of use for all of our users and employees, making the above a reality will be a huge win and game changer for many.
Finally with that, having a dedicated search to tags would be a tremendous step forward as well to go with the tag directory.
