I play on Game Pass, but plan to buy here. Having these goodies would be a great incentive to buy early.

It's only for sale on Steam, I don't want to buy it there.

The soundtrack can be found on Bandcamp.

https://maxll.bandcamp.com/album/spiritfarer-original-soundtrack

So what? What does that have to do with wanting it released on gog?
We want to buy a game and have the option to buy the OST/art in the same place. The fact that it's available on steam is insulting. Your know bandcamp is owned by epic right? So why even buy the game on gog? If the OST was available to purchase sans game, would you buy it on epic? Would you go to threads like this and link to epic? It's the same rationale.