It already exists in some clients but a huge % of people will get their first exposure through iris which i'm using right now since you can get a free nip05 here. The vast majority of people don't want porn in their feed (even if they like porn) and so if they see it here, particularly in large quanities we probably lose that user immediately. I mentioned twitter before, but it's algorithm means that unless you search for things, if you just keep pulling follows from whats hot, you probably won't see much, if any porn.