It's quite possible then that Koekoek doesn't have interest, but let's remember that Girodano is probably done sooner than later via trade, and Fleury just...is disappointing. That means if Soucy were traded, that leaves only 3LD who are any good and around for more than a few more weeks (or months). We could certainly entertain a piece other than Koekoek though.
Haydn Fleury still has upside and has played some strong games, he and Borgen have just been victims of the numbers situation in Seattle, and I honestly believe he would be ahead of Koekkoek on the depth chart here.
As for the offer, I just don't see where the incentive is for Seattle to make a trade like that.
Yamamoto is a bit younger than Appleton, but Appleton is still an upcoming RFA, and he has size, which Seattle desperately needs to add more of to their forward group... While I've never actually looked it up, but it would not surprise me if Seattle has the smallest group of forwards in the league. And yes, I know Yamamoto plays bigger than his stature, but he still can't really throw his weight around the way a guy like Appleton can.
And really, how much of an upgrade is Yamamoto over Appleton if Yamamoto were playing with guys like Wennberg and Johansson in Seattle. That is more than likely going to cut the production of a guy that has played regularly with either Draisaitl or McDavid - and at the same time, the drop off from Soucy to Koekkoek would be substantial imo.
Not sure Seattle and Edmonton make good trading partners, as Edmonton doesn't really have much in the way of extra pieces that check any of the boxes of what Seattle is looking for, which are available creative playmaking forwards, available forward prospects with top 6 potential, or available draft picks. Seeing as Edmonton doesn't have a 2nd, 3rd, or 4th available, and they aren't going to move their 1st for anything Seattle has to offer, the options are limited.