Disclaimer - I got no idea what Delta's going to do. But, I found a rumor / speculation thread with smarter than average participants (ie, one has "Managing Director" as a job title). Scott Hamilton has an inside track at Boeing and FWIW, he says, "No 777, no 787-10." Even if Delta were looking at used 777's, Boeing's role in ongoing certification and support would likely mean it would be on Mr. Hamilton's radar if it were likely.

Delta looks to double Seattle gates as wide-body decision nears | Leeham News and Comment

I'm a Boeing guy ... but here is the 330 sales pitch.

http://www.ausbt.com.au/files/A330ne...esentation.pdf