The outbox model is useless. All it can do is help you find posts from people you have already found (assuming you even WANT to see some of the things your followers post.) If you want to find good posts from strangers or find people with good content for you to follow then you end up adding a dozen relays whether or not you implement the outbox model. Web platforms are about the ideas and the interactions. A protocol that ignores any of that actual content will never work well.