>I think it's going to effectively kill public chat communities without either proof of identity

How? I have an identity. A state driver's license, birth certificate, social security number. I've even considered getting a federal license before, never bit the bullet. If I wanted to run a bot, what stops me from giving it my identity? How do I prove I'm really me (a "me" exists, that's provable), and not something I'm letting pretend to be me? You can't even demand that I do that, because it's essentially impossible.

Is there even some totalitarian scheme that, if brutal and homicidal enough, could manage to prevent this from happening (even partially)?

I'm limited to a single identity only as a resource constraint. Others more wealthy than I (corporations or ad hoc criminal enterprises) could harvest thousands of real identities and use those. Consensually, through identity theft. The only thing slowing it down at the moment are quickly eroding social norms (and, as you point out, maybe they're not doing that and it's not even slow at the moment).