In fact, Google already had a precursor to XEP-0352 called `google:queue`, but as I remember the stated reason for shutting down XMPP as being "spam"¹. Google apparently can't deal with spam in a federated communication system ...
¹ https://mail.jabber.org/pipermail/operators/2013-February/00... and then https://mail.jabber.org/pipermail/operators/2013-May/001680....