I really want to pick up the game and noticed on other plattforms there are also OST and Artbook dlcs.
I usually want to have things as a package and GOG is not good handling deluxe editions that are introduced later on.

So concete question would be:
Are the DLC comming to GOG as well?

If yes, will they be handled either:
- as dlc only
- as dlc and a separate deluxe edition

If deluxe edition that includes dlc is comming I will wait for it.

Reason I am asking:
I own a lot of games with all their dlc but the later introduced deluxe editions are marked as not owned making the store more annoying to navigate. Its a GOG thing but it made me more hesistant to pick things up directly.

I'd like to know the answer to this as well. It doesn't make sense to release a music-based game here, but release the soundtrack only on Steam. I don't want to buy the game here and the soundtrack on Steam; I want to buy both at the same store (here).

If you decide to release the soundtrack and art book here, then PLEASE use the bundle feature here like you do on Steam so those who purchase the whole thing here will get the same discount they would on Steam.