May I ask why? As I mentioned in the sibling comment, we get along well without it. Also, you could reuse Discourse code instead.
Another reason is ember-data is one of the reasons that I want to use ember-js. I would like to develop a program entirely on fronted then switch to backend. Without ember-data ember.js seems not that attractive to me.
It just like...after watching fire-up-ember-js podcast and found out the core feature is not production ready. I'm a little bit upset that I really bought the video..