Our publisher is looking into alternative storefronts at the moment, gog didn't accept Guard Duty sadly.
For people like yourself who backed on Kickstarter and want a DRM free copy I will make sure you get a copy regardless of which storefronts it's available on.
GOG is becoming more and more an embarassement, they reject many great games which would fit perfectly to their "Good old Games"-criterion (A Tale of Two Kingdoms and Grimoire come to mind but there are many more). A shame really. I find itch.io to be a great alternative to GOG.
I'm no backer but I don't like DRM of any kind. Now many indie-developer publish their games on Steam without the actual DRM (Steamworks), which is a good thing. For me, a game is DRM-free if I can play it (once downloaded) right out of the folder without any clients attached, being able to copy it to my laptop and play it there as well. May I ask if your game will need the Steam client to run in the background or if it will be DRM-free in my definition?
Thank you and all the best with your very appealing project!