I don't think it's about the language - it's about knowledge. A backend specialist can learn Javascript but may not know the nuances of working with the DOM, or optimizing for pagespeed, or the important front end libraries. Similarly, a front-end specialist may not have all the experience necessary to diagnose problems in a deployment. That's one reason I don't buy the "front end developers can now do backend development because of node.js" argument. Any sufficient competent backend developer can start writing Python code in a day. What that developer doesn't get in a day is understanding deployments, popular Python libraries, the ecosystem, etc.
I'm not saying they've removed specialists. I believe they still exist. But in switching to node, because client/server shares a language, they're now capable of sharing code as well. Which is what I imagine they are doing, which is why it's logical that they've merged teams. This doesn't rule out that front/back-end specialists are removed and become well-rounded rather, they're just working together more.
