Yo, just saw this on my tweetfeed so it would answer some issues:

http://ask.fm/WadjetEyeGames/answer/125721416822

QUESTION:
Sorry if I'm bringing up a potentially sore topic, but will the soundtracks for future games be available on GOG (either as part of the pre-order or generally)? I specifically didn't pre-order Golden Wake because there was no soundtrack on GOG but there was elsewhere.

ANSWER:
The GOG situation was weird. When I spoke to my contact there, I asked him what I should do about the pre-order because it seemed the community didn't like that I did it before. The conclusion we reached was to not do a pre-order on GOG at all, which was probably the wrong thing to do. This time around, we will do a pre-order. People might complain, but I'm not sure how else to handle that. I've asked GOG to make the OSTs available to buy on GOG but I haven't followed up with them. I'll be sure to do so. When my attention is mostly taken up by making the games, details like this tend to slip me by.

Regarding separate purchasable soundtracks, I think GOG is worried that will be viewed negatively since OSTs have been bonus content in the past.

Personally I'd probably buy game music here if it's cheaper than the actual game (since many games I probably wouldn't end up playing, but good music I try to find all the time).