Looks like the idea of sub-sub…categories in discourse was strongly debated but will most likely not be forthcoming anytime soon:
I’m not sure how discourse handles large numbers of sub-categories, i.e. visually in the listing or menu UIs. A related topic that considers an extreme amount:
https://meta.discourse.org/t/will-discourse-handle-this-6k-sub-categories/13698
It looks like subcategories can be reordered, so I imagine they could also be omitted from a “top listing” view?
https://meta.discourse.org/t/private-subcategories-on-top/35275/11
Think we may want to formally reach out to Discourse support about the last two points specifically for our use case.
Over all, I like the use of subcategories for designated projects, and then tags within it. And if a project grows so large to require sub-sub categories, then perhaps it would be time to bump it up to a normal category anyhow.