@reidrac@social.sdf.org @trinsec It was "subscribe with your reader", gradually (then all at once) replaced by follow/share "buttons" (trackers, actually).
I too use a reader now and it was helpful with staying away from Twitter. But lots of content ended up locked under spywalls. Old-school blogs are fine, but new services make feeds as an afterthought, if ever.
The XMPP situation is somewhat different, I think. The platforms leveraged their out of band notification channels to provide an illusion of real-time delivery on mobile devices. And then the network effects happened. XMPP made some extensions on the end. But it was too little, too late.