There is scant information available unless you're a subscriber to The Air Current, but this tweet from respected aviation journalist Jon Ostrower is a real mind-bender.
Link to his site/story:
https://t.co/vp1LLPVxyv
It makes some sense, in that Boeing Capital is the owner of most of the 717s, and some of the leases are coming due. I'm sure it's not a straight trade, I'm sure Delta still pays something, but it's interesting to see Delta trying to leverage its 717s into new MAX jets.