I’m not a fan of a three-strikes system, soft-locking accounts, shadowbanning, or anything that tries to be a warning and a punishment at the same time. If someone is repeatedly acting in bad faith like that, they tend to wear these slaps on the wrist as a badge of pride.
But more than that, I am vehemently against the idea of automating any sort of punishment. IMO, that kind of thing needs a degree of human judgement and accountability.
That’s a little off topic from the thread, so back to the point at hand: So long as anonymous comments are at least somewhat identifiable by mods (as I know they are), then I think it’s fine. If brigading really becomes a problem, I would sooner change it so that you have to be logged in to comment (as you do with voting) but retain the option for those comments to be marked as anonymous.