I’m not sure there is a case of Ember being the “wrong tool for the job”. It all depends on how much effort you want to put into the project.
I’m building a fairly large and complicated business grade enterprise app using Ember as the front-end. I could have developed it faster using HTML/jQuery spaghetti code but the benefits of Ember (URLs are important, maintainability, scalability, etc…) made it smarter for me to use it.
I’ve certainly run into several issues along the way. Form validations that don’t validate against a model have been problematic for me as have a lot of advanced UI interactions that are dead simple using jQuery plugins. Sometimes the Ember Way can be a bit convoluted but the benefits in the end are worth it.
I’m still not 100% comfortable with the framework and there is a definite lack of cookbook-esque resources compared to other frameworks like Angular or Backbone - mostly due to a Ember 1.x being available for less than year. As the community and Ember mature more resources will become available and guides/tips/tricks for doing things the Ember Way will become more prevalent. I intend on blogging about my experiences developing with Ember at some point in the future. I anticipate more and more folks doing the same as Ember gains popularity.
So to circle back around to your question - I don’t there is a definitive answer - you can build anything you want in Ember - it’s just a matter of if the Ember juice is worth the squeeze.