The email they sent unfortunately states:Please note, this promotion is only available on Steam
If that’s a case that really sucks. I will wait for official news before I start bugging Obs to figure out something or somehow move my order. I mean, it should be possible to generate keys for gog, no? Maybe a little bit more messy that steam integration, but come on! How could isometric RPG on GoG be the lesser edition?
Eric responded on Reddit and said:
Unfortunately, GOG isn't set up for promotions like this the way Steam is. However, we're looking into what we can do for GOG users and hope to have something soon!
Hopefully they work something out for GOG users.
While GOG might not allow linking user accounts from outside GOG the same way Steam does, they do support DLCs. Their answer is a bit weird, the system didn't have to require direct linking of the Steam account.
Could potentially have each unlock generate a redeemable code linked to obsidian accounts to use on gog and do it that way
either way following this thread for sure