That's curious. Must have to do with the size of the aircraft v.the age of the 717, because I'd thought the 717 had better economics.
I'd just as soon that DL buy the next 150 A223s off the line and be done with the T-tails, but...(I want something different when flying OMA-ATL!)
Allegedly, it has to do with fleet needs (the alternative role for the 717 as it's pulled from trunk routes; e.g. it's a poor fit on routes to small markets, particularly as mainline labor costs swell), expected maintenance costs, and the costs of upgrading/updating the aircraft (e.g. the cost to convert the aircraft to RNP-capable, the cost to replace the seats/update the cabin, etc.). Apparently, the ROI is being questioned.
I have no idea as to the credibility of this rumor, and I question the logistics and costs of DL being able to draw down nearly 100 aircraft in a short time period. That said, DL could probably replace the 717 fleet simply be deferring expected retirements, and adding minimal new orders. DL had previously said the 717 would be a flex fleet in the future, they could probably replace the entire fleet with about half the frames (or so).