I think it’s likely there are many types of communities that may exist across different apps, quite a few of which will take some similar shapes 
some will be super public and then it may make sense to have a fully public member list, some will be private and just within the app, and perhaps get some sort of management app like the Arbiter to control lists (or make them completely hidden).
But yeah I think there are enough similar shapes that it would be good to work together to outline what is likely to belong in those shapes. I really, really want to see interoperable communities across every app that wants to implement them in the Atmosphere
I mention it in this comment but I’ve got a meeting set up for next week to chat about requirements that folks already know of, if anyone is interested in an invite! [Discussion] What would help folks to see standardized? What are you itching to have answers on? - #3 by brittanyellich.com