Currently, on PC Early Access has only been announced on Steam.
I will take it as yes... I will also take it as no.
I worder if GOG DRM free policy might be a problem. Larian could be worried that disgruntled players would pirate the game and “provide feedback” without actually showing interest in it (financially). I could understand that. Or perhaps they want to keep feedback to one platform. Or GOG has much weaker infrastructure on developers end. Or they hate free market and consumer friendly business practices and have sold whatever is left of their souls to Gaben.
All are equally possible and most likely the true answer is something I didn’t think of.