On Google+, it was possible to individually block specific profiles.
This meant that the blocker wouldn't see the blockee's posts and the blockee wouldn't see the blockers, which is pretty much expected behaviour.
But on third-party threads, if a blocker/blockee were both commenting, others could see their comments but they'd be mutually invisible. As the platform matured and the number of such blocks increased, this reached a point where that platform behaviour became common enough that it was frequently commented on. If the thread host isn't sufficiently diligent in their own moderation (effectively each post author is moderator of that thread), it's also possible for such discussions to devolve quickly.
I guess Usenet would be another case where individual killfiles were often applied.
This isn't quite the same as your proposal, but it does raise the challenge that if there are multiple moderation regimes occurring, there is no canonical view of a discussion, leading both the potential confusion over what has or hasn't been said, and potential derailment (or similar behaviours) if a sufficiently disruptive participant is not universally blocked. The canonical flamefest after all is often just two profiles / participants responding endlessly.
Diaspora* is similar to G+, except that on third-party threads the blocks don't work, so that if A blocks B but C does not block B, then A and B will see one anothers' comments on C's posts / threads. This ... can be frustrating.
Oh, and the post-author-as-moderator model also somewhat resembles what you'd suggested, in that you could choose to participate on a particular profile's posts given that profile's moderation practices. I found that there were several people who did an excellent job of this, and who were quite affective, in effect, salon hosts, which was how I saw the G+ moderation model over time. This differs from what you suggest in that every participant on those threads had the same moderation experience, but it was possible to choose moderation practices based on which profiles' threads you chose to participate on. And I'd definitely avoid poorly-moderated hosts.