Could you give an example of your use case? As mentioned frequently in meta discussions, using more than two levels of categories is rarely the optimal solution. Usually, the same outcomes can be achieved through other means, such as tags.
To better understand your needs, I would like to ask:
- Does every topic really belong to only one category? If not, tags might be more appropriate, since a topic can be assigned multiple tags, but not categories.
- Are you looking to improve clarity, or are you also considering other factors, such as permissions or other rules? Categories can be set up with specific access levels, whereas tags cannot. As for clarity, they provide the same.