I think Boeing wants a DL 737 MAX 10 deal to pressure the FAA for an extension on the 737 MAX 10. But Europe may not budge.
I am surprised DL would consider the 737 MAX 10, given its heavy investment in the A321. A 737 MAX 10 will have a similar capacity to the current A321ceo, but the A3210neo with CabinFlex will have a higher capacity. All of the DL speculation on the 737 MAX pointed to the 737 MAX 8, which fits as a replacement for DL's A320s.