I've given a "Dark Steemit" some thought, tho' not for NSFW content as such: I was thinking more along the lines of stuff you'd see on 4Chan.

Unfortunately or fortunately, that would require forking Steemit and starting afresh. It's not a bad idea - back in tha day, LiveJournal threw up a dark-sister Site called "DeadJournal" :) - but it would require a large gang of cryptonauts to get something like that off the ground. For one, it would require enough folks to be witnesses...