Who told you they were going to hire in June? I have never seen anything put out by the company stating that. I have seen the following however put out over and over again. "We will decide on the possiblilty of hiring later this year based on the summer 13 marketing plan". That plan is still not out. When its out you can ask me and I will tell you if we will hire or not.
If I had to answer before the plan comes out I would say we will not hire. The worldwide economy is in the toilet. I don't see marketing pushing for any increases in block hours. The 717's and 737-900 don't really figure into the block hour plan much until the summer of 14. That is also when we really start seeing DCI block hours shifted to the mainline.
Keep in mind that Delta more so then other airlines has a huge debt problem mainly revolving around retirement. They carry that debt off the books. That is why the huge push to reduce on the books debt. Feeding that monster requires lots of cash. We can't afford any reduction in yield hence have to maintain more capacity restraint then other airlines.
Sooner or later a market share war will break out. When it does Delta will add capacity like the others. The industry will then resume its boom and bust cycle.