Agree with all the responses above.

I would only apply the GUC to the ICN-DTW segment as trying to apply it on the KE BKK-ICN won’t work due to fare class.

Assuming the ticket gets reissued to show you in OK or similar fare class (D1) the computer/agent should treat it as a D1 ticket and rebook you into D1. If the ticket is never reissued out of the P/A/G PS fare bucket, it’s unlikely to rebooked into D1. Even with the reissue, it might take some agent finagling, as with anything RUC/GUC related with DL. But you should be fine.

Ive made a 58 minute connection BKK-ICN-SEA before. Very tight, but doable. Boarding began as soon as I landed, and was well underway by the time I cleared transit security at ICN. Also, ICN is good at having greeters escorting passengers with ultra tight connections or delayed flights on arrival.

I’m also in the camp of avoiding KE when possible due to warm cabins, but wouldn’t totally rule them out if it meant a premium seat vs economy. I recommend wearing shorts if possible for any KE flight.