I don't know of any existing systems that offer everything you're looking for. Maybe we can start with something that meets most needs, and build on it? e.g., s

I don't know of any existing systems that offer everything you're looking for. Maybe we can start with something that meets most needs, and build on it? e.g., start with Reddit's code base. Building from scratch would be less desirable, and risky -- in terms of potentially killing the project before it even launches -- but it would also get you exactly the package you want.