Do you know of any Goodreads alternatives?
I like to discuss books say Pick out a specific passage from the book—a description, an idea, a line of dialogue—and ask members to comment on it
(Disclaimer: I am the developer)
(no affiliation)
If you are interested in building such a product yourself and want to approach it more from the multiplayer document annotation platform angle than the specialized book forum angle the Memex, Ted Nelson's writing (especially Literary Machines) and Wikipedia's reference templates are also worthwhile sources of inspiration.
That almost sounds like a class structure type thing. And, I find even with a jenky interface and feature set I tend to gravitate towards social networks with a population past a certain threshold. I couldn't tell you that threshold as a number, but it's got a healthy glowing feeling, like everyone is contributing regularly with sincerity and enthusiasm. That kinda stuff that grows mostly organically.