I personally feel productive with Ember, but the custom object models and getters and setters for everything are a bit of a turn off, especially after working on an Angular project recently with typescript support. Mobx, for instance, seems to be able to accomplish similar things as Ember but without the custom object model and getters/setters.
[1] For those wondering, Glimmer is Ember's next iteration of view layer and rendering engine, pulled out into a separate library. It's built from the ground up (and so isn't subject to backwards compatibility with Ember just yet), uses typescript, is component based, and it compiles down to op-codes that are used to update the DOM instead of DOM-diffing. http://glimmerjs.com/
Ember never made it to that point and almost certainly never will. People are still free to use it of course, but it’s going to be a poor technology choice in light of the above factors.
