While not directly related to DL, thought it was relevant enough to share:

DL ticketed/marketed passengers traveling on KE operated segments can now pre-select meals departing Korea. (They are not available on flights operated by KE inbound to Korea). Simply use your KE PNR (found either by calling DL or using pnr.sh) to look up your reservation on the KE website and select your meal.

Previously this option was not available for codeshare segments, but has now been enabled. Successfully (or at least I think successfully) chose meals tonight for ICN-BKK in early November.