I really wish XMPP had taken off. Perhaps the most important place for standard protocols is in chat applications - i.e. how we communicate with each other electronically. Email is unlikely to go away but if I want to communicate with all my friends I need:
* Google Hangouts
* Facebook
* Twitter
* SMS
* Whatsapp
* iMessage (cost prohibitive)
When really I should just be able to log into xmpp.voltagex.org and talk to everyone.
(Also, why isn't there a standard for "dialling" email addresses yet?)
GChat used to use XMPP, as did Facebook IIRC. I also remember reading that iMessage uses it, and HipChat definitely uses an extended version. These could all be made to work together, but how would that keep users on the site where they're force-fed ads? It makes a little less sense in the HipChat / iMessage use-case.
Basically the same reason that little is available via RSS these days, and what is always has the "click here to read the whole article on our site, where we can show you ads!" after a few sentences / paragraphs.
Actually, you can do SMS, Facebook and Hangouts in one app.
There are SMS services who support XMPP, and additionally Facebook and Hangouts support the XMPP client-side. It’s not as convenient as sending from kuschku@chat.facebook.com a message to justJanne@talk.google.com, but it still works quite nice.
Or not.