I'm still wondering why all the initial Dealer content (that was already in the game mind you) was cut?
Well, it seems he just considered that she didn't fit right now. This "remake" of sorts is clearly way more story-based than the original demo, so he is orderly introducing elements into the game as they fit. Just by watching the new introduction, we can see that Numeric has great plans for Dealer at a later stage, and so it's my guess that it won't be until then that we will fight her.
In my opinion, it's not only a very reasonable decision but quite a good one, because we all know and love Dealer by now, and by reserving her a nice place in the story later on, he's building anticipation for what she has in store for us, and I can't wait to find out.