XMPP is a bad example. Google Talk (https://en.wikipedia.org/wiki/Google_Talk https://en.wikipedia.org/wiki/Google_Talk) supported XMPP from 2005-2014, but by

XMPP is a bad example. Google Talk (https://en.wikipedia.org/wiki/Google_Talk https://en.wikipedia.org/wiki/Google_Talk) supported XMPP from 2005-2014, but by the time they dropped federation, it had already massively declined. You can argue over the reasons for that, I personally blame a combination of smartphones (iphone launch in 2007), which drove phone number based messaging apps/iMessage/WhatsApp/etc and the rise of path-dependent social networks like Facebook (FB messenger) However, even if you look at the pre-2007 pre-FB era, instant messaging was dominated by Yahoo Messenger, AOL Messenger, MSN Messenger, etc. None of them supported federation, there were several attempts at interop, but none of them wanted it. Moreover, IIRC, Google's stated reason in 2014 for dropping federation was a non-reciprocal leaching that some of these platforms were using to exploit XMPP federation to ingest users into their walled gardens. In messaging, every single product Google has offered has failed to gain market, and it's really Facebook and Apple which collectively have a oligarchal stranglehold on the market (or WeChat in China) Google's latest attempt is a restoration of federation on mobile through RCS, but what's the likelihood that the dominance of iMessage and FB Messenger/WhatsApp are going to be weakened by this?