> Also seems motivated by the desire to keep Rails relevant, but without actually trying to evolve Rails towards being more useful for client side driven apps.

IME, there isn't a smoother way to implement a bunch of RESTish json endpoints hooked up to a database (resources) and have dependency management and compilation for your frontend js/css (via the asset pipeline).

There may be other frameworks out there that make serving up and delivering client-side driven apps easy, but I haven't heard of them.