I think it's supposed to be a shift from backend/frontend to frontend only, in the same way that Heroku was a shift from building your own infrastructure to just building a backend/frontend. By reducing the surface area, you can reduce the required tools and platform knowledge and reduce the development friction, in theory.

There are plenty of unanswered questions, but I can totally foresee this sort of thing as a viable development platform for some projects in the future.

I've been playing around with backbone.js and it's really promising, because the server acts only as a REST api.

It was a paradigm shift for me. You should try it.

we have / do it when it makes sense (heavy client). Either way we require much more infrastructure for "real" apps than some black-box backend, zmq clusters for computation etc.. I guess this might be an ok playground for some trivial apps