> pretty technically feasible

Not only feasible, it's extremely easy to do these days with things like React (+Redux). We're about to launch a fairly large project for an Australian broadcaster using this approach and it's been incredibly simple to do.

And there's nothing ~magic~ that React does to make this possible - it would be quite trivial to 'roll your own' framework for this. Best of all, you could start with doing it just server-side and then roll out the JS to 'the other side' later on.