Hmm, it's a tricky one - sunrise/set is such a sharp gradient from dark almost black burnt orange to a bright yolky colour. The beauty of the Firewatch wallpapers, etc. is that there are lots of layers in between those two and it'll be tricky to get those colours working in keycaps, hence why we've not seen a set like that, I'd wager.
I think you're right, KAT Eternal is about the closest you can come to that kind of gradient, just in a night theme.
This is the closest I could come to something quick in KLE just by picking the colours from that wallpaper:
(I think I'd call this set something like GMK Rise or GMK Magma)
The main problem is contrast, in my opinion. White too bright on bottom row legends, fine for the rest, except for the top. You'd also have an issue on ISO, I'd say, with the enter key crossing two rows. You always get that problem with horizontal lined sets, which is why you don't get many.