One nice thing would be a "Related Subreddit" spot on every post's comments. These can be user added and voted on based off of relevance. Page admins would be able to disable their subreddit from showing up in these if they are trying to maintain a smaller community, but otherwise anyone can add to the list. This could be a way to find new subreddits that are related to the content you are reading without having to sift through the comments hoping someone recommended the author to crosspost it there.