This is my feeling about Rails. I've created several Rails apps that delighted the customer, and most have required literally zero maintenance after years of use.
Sprinkle in a bit of jQuery and you have an app that is stronger and just as fancy-feeling as a mess of a massive client-side app.
I think the improvements to turbolinks in Rails 5 make pjax more of an option now. Also, for scaling remember it's not the end of the road for Rails when you're running out of processes to keep up with requests. JRuby 9000 has been gathering a lot of momentum recently and promises huge performance gains when Truffle and Graal kick in. Migrating a Rails app to JRuby is not that difficult.
Sprinkle in a bit of jQuery and you have an app that is stronger and just as fancy-feeling as a mess of a massive client-side app.