Here's my LR only vignetting removal attempt on clickclick's file from above.
Here's the top two corners tackled quickly in PS with Content Aware Fill (bottom sea corners left for comparison);
It feels like it's presenting a lot like the HD DA 20-40, the vignette is tackable, and in some instances a small crop of 36mp down to 30mp (keeping 3:2) would likely remove the vignette if preferred to visiting PS.
Many of my FF HD DA 20-40 shots I have not even tackled vignette because it compliments the image. For me the places it mostly stands out and seems out of place is exactly the kinda scene that clickclick showed (and then passed onto me). Vignetting in the sky is often a real turn off for me, however some land vignetting in the bottom corners never feels quite as problematic. I've learned to just be a little mindful of where vignetting will be necessary to tackle in an image, and thus if 28mm feels about the right length then I go a tad wider to 26mm or so and crop in so that the end file is something like 30mp (this is the quickest and least painful way to approach it). Or... frame the shot with the intent to make a 4:3 aspect ratio picture instead of 3:2.
I really wish the K-1 had more than Full, Crop and 1:1 for modes. I'd love a 4:3, 16:9 etc etc. Crop just feels too much of a mp killer and overkill for so many lenses that are deemed unsuitable in FF mode. Can you imagine how many more lenses people might use on the K-1 if the review stated that the lens was fine for 4:3 and 16:9 images etc? Right now we judge the success of a lens on 3:2 which I understand however I feel should not be the be all and end all.
I can see from tracking the lens should be delivered today, oh happy days