As already pointed out it's THQNordic and not its subsidiary Deep Silver that's publishing this so there's no reason why it shouldn't be available on GoG in 2020. Maybe not on day 1, but eventually.

It would be nice of THQ Nordic and GOG to throw up some store pages for these recent reveals, since we all know they'll most likely have a simultaneous alongside their Steam counterparts.Not the same company, but Baldur's Gate III got one at least.