For the record...
Purchasers of the Special Edition on GOG currently can download the Propast Map and Artbook for Book 1
Plus the same Wallpapers Kickstarter backers have had access too for a while and some Avatars
The rest is not yet available there either
This is now what Kickstarter Backers have in Humble store as well (except avatars, afaik). (if any backers wants to know how to get the extras in Humble, see this image file)
So the "Journeys birth" is apparently delayed for everyone, backers and purchasers, on Steam/GOG/Humble.
Sorry if that's not helpful, but at least you're not alone