There are times when a model belongs to more than one subcategory. For example, some useful household models can also be decorative. As is now, one can only choose one subcategory.
To prevent widespread spamming, put a cap on the number of subcatogories one model can choose, such as a max of 3. If necessary, add in penalty for intentional abuse of the feature.
Even with additional subcategories, the current category list falls short. It would be better to eliminate categories altogether and focus on enhancing tags. Tags could effectively handle all our needs for search filtering, grouping, and exploration.
It’s not an either-or proposition between categories and tags.
Many times users don’t necessarily know what they are looking for. Browsing is one of the main traffic sources.
Related: I recently proposed an improvement on the subcategories under the Household category.