On the Google side the XMPP federation got killed when Google Hangouts and Google+ became the core strategy. The company wanted to focus on "social" (but their own social network) and didn't care about other chat. Back then I worked on the App Engine team which had a XMPP Chat API. When GChat killed XMPP Federation that API lost the majority of target users as a result. I tried to make the case for maintaining XMPP support - taking it up with some VP of Engineering. Alas, nobody cared about the opinion of this random guy in developer support (~2012, early days of Google Cloud)

You forget that Google was worried about other XMPP services stealing user data. If I remember right, some services (maybe it was FB) was not sending out all data to Google in the federation system (I forget if it was names or friends lists or something). So it would allow other services to ingest data Google was sharing, but the sharing wasn't reciprocal.

Can we make XMPP popular again? We really could need an universal internet standard for IM.

There is hope. The European Union's Digital Markets Act allows new messaging platforms to demand interoperability with the existing walled gardens. All it takes is for other jurisdictions to follow suit.

You can't use regulations to change physics, and (demands or no) it is unclear what sort of interoperability is really possible.

What will really happen is that there will be some subpar common denominator. An existing "walled garden" (WeChat?) would add support for this as well.

But this would wind up being rather insecure, because messaging services tend to use email addresses they don't control or phone numbers they don't control as identifiers. We'd have to wait for carriers and email providers to be regulated with the burden of solving this mess (for markets they aren't in).

Yeah and how did that work out for google? Hangouts was their most popular product and most of my friends were using it. Incredibly stupid management decisions right there.