You can operate your stellar-core in two modes, validating or observing. If you are in validating mode you are both listening and participating in consensus.
But semantics aside, in Stellar anyone can participate in consensus. As in anyone can both listen and talk. It is true that maybe no one else will want to listen to you but there is certainly no barrier in the protocol keeping people from talking. And again if there is some cartel or some group that people feel are getting too much control it is trivial to set up your own nodes that are fully participating in consensus and have the non-cartel nodes listen to each other.
This is simply not how reality works when it comes to namespaces, and supposing it were, it would also be bad, because in both instances you are sacrificing security.
In the first instance, where a cartel is formed, the namespace is fully controlled and censored by them.
In the second hypothetical scenario you raise, where a second cartel is created over the same namespace, you have a global conflict over the namespace and effectively a group-based MITM attack. In other words, the total destruction of consensus.
So in both instances: Bad Things.
Also I'm not sure what people have in mind for the IETF ILC thing
You may want to pay attention to how your software is actually going to be used.