My 1 question, is how do you want to differentiate "community" subreddits from "fap material" subreddits? Ideally, I think they should be categorized too, but denoted in the list that they aren't intended for porn. Another example of this might be the old sextoys subreddit where people asked questions about toys.
I feel that having its own top level category would be less organized than having it in line. Maybe doing something like:
Let's take Lucky Pierre for example - it can contain mmm, mmf, fffm, mmt, mft, and a whole variety of other variations.
Should it just be under a bisexual umbrella? What about the all male or all female content? Or all trans? It doesn't fit into a clean category, but individual posts may.
So some may need to go under multiple categories with this structure.
This is trying to be like reddit's NSFW411, which used hierarchical categories. Tags would work better in a lot of ways, but that would require a different format. Ideally there'd be some way to have a hierarchical structure for tags and each comm can have multiple tags, but I'm not sure how to implement it here.