This will at the very earliest happen when/if Twitch moves away from IRC. But even then I don’t see Twitch pulling anonymous chat for a livestreaming platform. The amount of actually valuable signups will not increase if you lock the main feature streaming platforms have over just normal VODs (Chat), compared to just giving people access and allow them to create an account for convenience if they do like the site. A forced signup isn’t what you want, you need people that will actually watch content, ads, pay for subs, the people that make you profitable. And if you drive away a portion of potentials there and instead get a ton of inactive forced singups, I can’t see the benefit there.
They might lock it behind some first-party endpoint and not document it, but like the follow and mods/vips endpoint, if anyone wants that data for malicious purposes they will just use GQL anyways, who cares about some TOS at that point. And the stuff you are talking about, like C&C bots, they will for sure just go ahead and use some 1st party stuff.