> There's a reason that these alternatives are winning.

Yes, and that reason is that the current crop of up-and-coming developers have the same problem as past generations: They'd prefer to implement their own solutions vs. looking to the past.

Slack just happens to be the current darling in group communication. At some point, someone will make something that will change the fad-diet to The Next Big Thing.

I don't agree. Literarly all FOSS projects I am part of are on IRC, and those are quite many. I literarly never have thought: "I wonder if there is a slack chanel for that FOSS project", per default I look for the IRC server and chanel name. When I read articles like the OP I always wonder which FOSS projects they are using.

Here is a list with the projects of the top of my head with which I'm in contact via IRC (quite often): Firefox (+OS, +sync), Qt (+Cpp, +QML, +QtCreator), Sailfish OS, IndieWebCamp, foss-gbg, golang, SELFHTML, Thunderbird, Clementine, Gnome (+calendar, +addressbook, etc.), Gimp, SyncThing, VLC, ArchLinux, ruby, Emacs, node.

> IRC's time has passed.

I wouldn't go that far. Freenode is bustling.

A lot of the alternatives are mostly extensions to the IRC concepts though (group chat, #hashtag, private chat, mentions, etc..). If all you need is text, IRC is fine.

I actually use a number of things through BitlBee [1] just to combine everything into one client. Scripting things in python is also fairly useful.

[1] https://www.bitlbee.org/main.php/news.r.html

I don't know if the time has passed as much as people can't get through the barrier of entry technically?

I still use it every day, just as I've done for the last 20 years.