irc is alive and well. I don’t know how much traffic on usenet. telnet is peer-to-peer and a massive security hole. Talk/ytalk is simple irc-like interface, not secure.
There are many different communication models. Scaling up is not easy to do well.
I’m very active on IRC and NNTP. Telnet can be made secure with SASL. It’s a terrible protocol natively but like SMTP can be made functional.