PubSub alone isn't a great replacement for NNTP. (It's maybe a replacement for SMTP.) The reasons for an NNTP 2.0 (as mentioned above) are more about storage/forwarding, if you want access to the back history as opposed to just live updates. You can build such things on top of a PubSub protocol, as ActivityPub is at heart still a PubSub protocol, but has a lot more storage/forwarding concerns added on top, as an example.
Fair points. I wasn't aware of any of these tools, but then like the majority of the world I haven't actively used XMPP in years (which is obviously among its largest cons today).
My intent wasn't to diminish your initial comment, just that a protocol is a technical answer to a problem that is more probably a societal one. It takes time and effort to commit to another communication protocol, especially when it's not the core of what you're doing as a project. Maybe what is needed is not just a protocol but proper tools to make it easy to use (and the bar with the simplicity of email is very high)