If Apple had kept their promise to "open" FaceTime, I wonder if things would be different. Imagine being able to open a Hangouts session with anyone in your contacts who has an iPhone (without them installing Hangouts for iOS). Imagine if the Hangouts protocol had been released, then I could keep my strange bitlbee setups and have my messages anywhere.
I think it's probably time to move on from XMPP, but you really need Google, Apple, Microsoft and WhatsApp in a room together thrashing out something that'll work for everyone. I can dream, right?