In terms of XMPP, I checked yesterday. After updating the Android Talk app to Hangouts, all of my XMPP contacts disappeared.
In terms of email, using Google Apps on a custom domain would avoid lockin and actually not be a bad choice, at least for now. I went with Fastmail anyway, and I think it's just a better service.
For XMPP, it's the Hangouts app that I was referring to as the "new chat system". Federation for regular google talk was turned back on, but you'll need a third party XMPP client now, I guess. Fortunately they're quite common.