My last sentence kind of expresses my whole point: "the writing is on the wall". I think that what's left of their XMPP support will be phased out sooner rather than later as everyone jumps ship to the new platform.
That they terminated their app (Google Talk) on their leading platform speaks volumes about where XMPP is going.
To add fuel to the fire, I think Google Voice as we know it is going away, too. :) I can't see how they're generating worthwhile profits on it.