I think the setup you describe is similar to RSS: an individual broadcasts information on their channel, and other people can subscribe to it with their own cli

I think the setup you describe is similar to RSS: an individual broadcasts information on their channel, and other people can subscribe to it with their own client. There are no public keys involved, but being able to push to a specific RSS feed should be enough proof that the sender is who they claim to be. If that answers your first question, you can read further essays on why RSS did not work as well as people intended. I don't have any specific one in mind, but I'm sure you can find some easily.