I just did this, HNL to BKK. Only looking for upgrade to Business though.
I'm a Delta Plat and I could not get any seats through Japan, end of Oct is the end of their vacation season. I'm an Expertflyer subscriber so I went online to check all this. Used the Skyteam search and saw lots of KE, did a specific search of appropriate flights and saw lots of M/B/Y/Z buckets. KE shows max of 4.
Picked dates that had availability, then called Delta with those specific dates. They struck out on DL flights. I suggested KE after we discussed the whole Japan vacation thing. She immediately said no availability. I kept talking to her, knowing they were there. My plan B was to hang up and try another agent later.
But....she "found" the seats, and, this is the ICE CREAM, she booked the "B" seats at a reasonable fare, less than my last DL. 25,000 miles each way upgrade fee, and can't confirm specific seats till within 30 days of departure.
My only concern is what my Medallion qualification scenario is. I was assured by the agent that I will earn "100 %". Well with Delta I do better than that, so we shall see.