I just remembered this while responding a thread just now, but there is a program called GOG connect that adds participating games to your GOG library if you already own them on steam.
I think this would be a pretty good solution to the GOG controversy, I thought about giving backers keys for both, but realized we could give them to other people and WarHorse could lose sales. This issue is avoided with GOG connect. I personally don’t think it’s unfair, since we already own the game it’s not as if more than a couple of people are going to buy it on GOG as well, and it makes everyone happy.