Regarding Ruby: single-page apps vs. "Turbolinks" [updated]

The Ruby/Rails folks are taking a stand! It seems a major focus of Rails 4.0 is to empower users to create server-side applications that are as fast as client-side JS/JSON (single-pagey) apps: Rails 4.0b1

Their messaging reflects a belief that delivering dynamic HTML from the server is superior to pushing it all to the browser and communicating only via API. I think I might kind of like this. It can get messy when we cede control to the browser via single-page apps. Of course, much good work is being done here, but it's all too easy to expose security risks, or just business-logic inconsistencies, when the content doesn't really exist until the browser chooses to create it. And with today's browsers pushing updates every other minute... oof. Future-Dave, let's keep an eye on this one.

Update: I spoke to a friend who's a Ruby expert and has a very practical brilliance. He's not a fan of Turbolinks, and predicts it will be a massive failure. DOA?