A year ago I did hear from my travel agent, who at the time was the primary contact for Delta reservations and news, and was told that DL had plans to re-start it's service to SEL. I use to fly PDX-SEL frequently in 1998 and 1999.
KE and DL are already in the "Sky Team" alliance, which allows one to accure miles on both airlines in a single frequestn flyer programme. I believe there are already code shares.
Korean Air seems to offer really cheap fares to Asia from North America quite frequently. If you like their service, then I would take advantage of the fares. I'm sure many people can provide some trip reports regarding KE's inflight service as well as tips for making hte most of your flight.
I am not a fan of Delta, nor their inflight service either. If you prefer DL and are able to pay the fee for business elite seating, then it may be worth it.. otherwise you might want to stick with KE or another airline for that matter.
I guess you'll have ot wait and see when DL plans on flying back to Inchon, because they dont seem to tell anyone much about their plans. I have only been able to find out the same info as anyone else on this mesage about DL returning to Korea, and nothing more.
In the past DL flew MD-11's to SEL, and they also send those aircrafts to NRT and NGO at the present time. I would imagine that they would stick with MD-11's, as the 777's seem to be more viable on trans atlantic routes compared to trans pacific routes. I have also heard that hte seating on the 777's are very uncomfortable.
For more info on Inchon, pelase refer to this message thread: http://www.airliners.net/discussions/general_aviation/read.main/384111/