Seems to me like this is reinventing parts of ember.js on top of Backbone. That's neat but when my apps need this sort of behavior I'm willing to be they will also need solutions to other common problems and I'd rather not reassemble a large framework out of disparate pieces to get that level of functionality. When do you decide that you have so many layers on top of Backbone that you have a custom stack no one else will understand?
Could someone give a practical example of a use case for this? This is probably useful for some typical problems in Backbone applications but not something I knew I would need (having built a couple of non-trivial Backbone apps).