I just redeemed one of the keys from my kickstarter account and noticed that none of the extras were added to GOG. Am I able to get the digital collector's extras (map, soundtack and so on) or would I have needed to active the key on Steam?

Same here, activated some time ago and I thought maybe they get added when the game is released but I still don't see any extras.

Considering the full release is happening right now, I would surmise that there might be a small delay in the "goodies" appearing on one's account. This is possible given that GOG's servers are under heavy load and the staff are super busy. That said, I recommend giving it a bit of time and then getting in touch with GOG.

Kickstarter rewards are nothimg to do with GOG.
In my experience they are often provided on GOG, but not always.
It's the devs you need to ask about that one, and providing the game itself will be their first priority.

I just got finally my D:OS2 edition upgraded to the Divine Edition as I got in my Larian vault just a key for the regular version. Thank you very much for this Larian. :)
The only items I still don't see listed from the CE are the following items:
- Behind-the-scenes Footage
- Digital Art, Design Docs & Story Notes
It seems like I can't download them in the Larian vault nor are they listed in the Divine edition in GOG but they are mentioned in the Eternal edition.

Raze? Can you or anybody else please confirm if those two items are part of the DE even they are not mentioned on the GOG store site?