Lots of good info on fleet plans on Delta net. Couple of highlights or lowlights depending on your point of view. Wide bodies in the current RFP will start arriving in 2017. 747's will be replaced first then the early 767ER's. Hints that they don't want a 380 seat replacement for the 747 so will be smaller. 50 aircraft buy initially. Overall smaller airframes for the Pacific and bigger in the Atlantic seems to govern what airframes they will be buying.
757 will be downsized to about 75 airframes. Those will be retained for quite some time. A321 is not a true transcon aircraft and can't replace the 757 in those markets. 757 and 737-900 will do the transcons. 10 to 13 million each to overhaul a 757. They love the airframe but that amount better spent elsewhere. 75 total airframes will cover the routes other types can't.
Love the MD88 and ours sons will be flying them to their retirements! Super cheap and fuel not a huge issue on shorter flights. Buying used ones for parts.