So glad this will be default in Rails. I spent ages building a custom version of the same kind of PJAX framework, using headers to transmit flash messages, interpreting XHR calls in new and exciting ways, etc. It really needs to be standardised for modern web apps.

If Rails 4 is all about PJAX, my hope for Rails 5 is it's the one that embraces fat-client JS apps and exposes JSON services in a standard way, so they can easily be consumed by convention-based frameworks such as EmberJS.