On Steam there is a 'Premium edition' that includes "Original Soundtrack (41 tracks), 8 audio books (160 minutes total running time) and a wonderful game comic by Olga Andriyenko". Are these included in the GoG version or, are they available/going to be available on GoG?

The current GOG extras are just wallpapers, avatars and artworks. At the point when TNotR was released, GOG didn't sell (IIRC) multiple editions of one game, so Daedalic went with the optimal price solution (quote). This seems to be changing nowadays, so maybe there's a chance of the Premium edition appearing here.

Thanks. That's a shame, I'd like to get the premium edition DRM free but, I'm not fussed about waiting (have plenty of great games to play in the meantime) so, I'll wait and hope it's available on GoG in the future.

Ya, I was disappointed the complete version is only on Steam as well.

I just become aware that a premium edition exists and I created a wish on GOG to include it. The name of the wish is "The night of the rabbit : Premium edition".
I hope this will come true.

Because nothing is impossible.