Ember.js is extremely future-proof. Yehuda Katz, who I work with on Ember.js, is on both the W3C and TC39, the committee designing the next version of JavaScript. Needless to say, we have a pretty good idea of what's planned for the future of the web platform; we're also very involved with the standards bodies to make sure it is as powerful as possible for building web applications.

Setters and getters are a trade-off. While we'd prefer not to require them, the alternative is that you have to diff objects every time a change happened. And not just a change, but a possible change—which means in response to almost any event. By using getters and setters, we avoid this particular performance footgun.

Actually, Ember views have much more in semantically common with Web Components than Angular directives, despite the fact that many people like to repeat this misinformation. For more, see this thread on Google Groups: https://groups.google.com/forum/#!msg/polymer-dev/4RSYaKmbtE...