tl;dr: after pushing rcs so hard for years, killing hangouts well after forgetting about it, & hiding it from gmail, google now wants you to use its (and google allo’s) successor, google chat.
I’ve seen a lot of buzz about XMPP lately (well, mostly in relation to P92 and corps killing FOSS projects). Beyond it being a comm protocol, I don’t really know much about it. Is it still in use?