Will GOG ever get the OST for Grim Dawn?

I know you are asking about GOG but in case you or somebody else does not know then you can get the OST here as well:
https://skewsound.bandcamp.com/
I think it is amazing :D

Or simply buy them direct from Skewsound.

http://www.skewsound.com/soundtracks/

If you've purchased the game, there is no need to purchase the soundtrack separately - just extract it from the game data using the tools included by Crate.

To do this, open a command prompt window and navigate to the folder where Grim Dawn is installed (by default C:\Program Files\GOG Games\Grim Dawn or C:\Program Files (x86)\Games\Grim Dawn) and type the following:

archivetool resources\Sound.arc -extract %TEMP%

This will create a copy of all soundtrack data (over 3,000 files) in your temporary folder (C:\Temp by default - change %TEMP% to refer to another folder if you prefer). The music soundtracks should appear in a Music subfolder allowing you to copy them somewhere more permanent.

For the expansions, use the following commands:

archivetool gdx1\resources\Sound.arc -extract %TEMP%
archivetool gdx2\resources\Sound.arc -extract %TEMP%