Ston's stuff is pretty easy to interact with. Drop a can for him to pick up, then either let him have it or blow him out of the sky when he goes for it. Or you could steal the people when he's trying to grab them. Or you could even help. Post-Retribution it'll get even more interesting.
Specific example aside, I think one needs to differentiate the type of activity going on and how that affects how others can participate: if what you're doing is in space, even if nobody is actively doing anything it's still very possible for them to help or hinder as they desire - and so I wouldn't really consider that situation an echo chamber because the only reason it's echoing is that nobody's gone and done anything about it despite it being possible to do so. Even if the IGS thread is just him prattling on and on and on day in and day out about some random jerkwad of the day who dumped a can of people at a gate rather than be fined and penalized for carrying contraband.
If the activity is in a channel then it becomes more difficult. Most people will avoid RPing with people they don't feel they're going to get a productive experience with - regardless of the outcome of the session - and will prefer to spend time with people who they feel will produce that experience instead, even if the person is playing an antagonist-like part. I don't think that necessarily means that it's an echo chamber, however: just because the developing plotline is going on "behind closed doors" doesn't mean that it cannot be influenced (deliberately or not) by outside parties who aren't necessarily involved, nor that the intermediate or end results of the plotline won't have an affect on outside parties.
In your case, Silas, there are ways people can interact meaningfully with your thing - people who are more aligned with Omir could just wardec you or hunt you in space, and people who agree with Silas could hunt those people in response, etc. - lack of interaction so far just means there hasn't been anyone who wanted to stick their hand in the pool yet, not that the pool is blocked off with razorwire and landmines.