> Let the browser maintain a DOM tree that templates over a JSON object, then reactive-ly update and it's an amazing experience

Totally agreed. I even pulled off an Elixir library as a POC to show this concept, here's an example project: https://github.com/surferseo/live_data/tree/master/examples/... (most relevant part of API is here: https://github.com/surferseo/live_data/blob/master/examples/... and here: https://github.com/surferseo/live_data/blob/master/examples/...)