Matrix offers the best of both world: federated self-hostable servers, decent UX and the option to E2E-encrypt entire channels.

Notably, Mozilla has switched from IRC to Matrix.

The author of the article explicitly waves off IRC and offers some good suggestions at the bottom of the article.

(More than privacy concerns, a major concern for IRC in this era of mobile devices is protocol chattiness. Phones save battery power by minimizing messages per second required, and IRC's protocol isn't designed to work well with that architecture).

Yes, that is true. (However, for private messages, if you and the other person share a key, you could encrypt the messages before sending them. For public messages, the intention is that someone can read it, so someone being able to read whatever you put through the service is an intentional and desirable feature.)

But since this communication is public, anyone should read it if they want to do, so IRC is good.

Telegram?

Proprietary & closed source

Not end-to-end. Telegram servers see (and log, this is in Russia!) plaintext.

1) In the context of a public discussion channel, end-to-end encryption and plaintext logging are features. Their presence means that a person is able to join and see context. This is good.

2) Telegram is not based in Russia. In fact, it's been intermittently blocked in the country.

I am corrected.