I'm surprised Facebook Chat still works for you? My understanding (and others' experience, from a quick Google) is that XMPP Chat has been disabled since earlier this year: https://developers.facebook.com/docs/chat They only supported exactly as long as they needed to to gain market share.
And Apple gets pretty much zero kudos from me for client XMPP support. iMessage is a proprietary walled garden; client-only XMPP support is simply their one-way valve to get people into their network and only ever had any worth because Facebook and Google used to support XMPP.
I was surprised too, but it works, minus offline messages. (I am using it right now). Do you really think Facebook ever needed the market share from XMPP? I've always assumed that Apple and Facebook only support XMPP because they use it internally (engineers being engineers...)
> And Apple gets pretty much zero kudos from me for client XMPP support.
I guess we have different expectations. Apple is a company that sells me client hardware/software. I use Mail to connect to standard IMAP servers, I use Messages to connect to a standard XMPP server and Facebook. You can apparently even buy Apple's XMPP server through the Server app on the App Store: https://en.wikipedia.org/wiki/Messages_Server
The one thing they don't offer is a single, centralised XMPP server. That's not really an active attack on the standard, though.
Anyway, I live in a completely different filter bubble than you and your sibling poster - XMPP never had any momentum at all around me, so I can't really speculate on how it died.
And Apple gets pretty much zero kudos from me for client XMPP support. iMessage is a proprietary walled garden; client-only XMPP support is simply their one-way valve to get people into their network and only ever had any worth because Facebook and Google used to support XMPP.