The world was a better place with Jabber/xmpp where we could setup our messaging system and don't rely on closed systems like we do today as Whatsapp, Telegram, iMessage, etc. iirc Google deprecated support for it in Google voice long time ago which marked its declined
The blog post you are referencing explains the changes the XMPP community has to do to keep up with what Lets encrypt did. TLDR: People just need to upgrade their servers.