I only have a peripheral knowledge of Twitch, but don’t they have a similar solution to what you’re outlining here? There is a “public” channel, on major streams this is full of spam and nonsense, then a separate channel for subscribers where they can talk amongst each other.

Perhaps a subscriber-only gate to comments would be a good thing. And only subscribers could read the comments, too. Channel owner is tasked with moderating the conversation or recruiting mods to do it, like any chat room or message board. Then, whatever happens in the comments becomes the channel owners responsibility.