I played the demo and I really enjoyed!
And I plan to buy the game anytime soon.
But before I buy it I have a question …
If I buy the game, I get serials, and say that the game came into steam (after I bought the game),could I play the game through steam with the serials I received when I bought the game?
I don’t have the link to the thread(s) where they have said this, but I’m sure someone else can pull them up to back me up on this one.
What they’ve said regarding Steam is that if You purchase it through their site, when(/if) it gets greenlit and is able to be released on Steam, anyone who has purchased the game through this site will recieve a steam code for it(Currently when You purchase it through the site You recieve a .exe file).
So yes, if You purchase it through here, once it gets onto steam You should recieve a code that will allow You to install the game inside of steam(in the meantime, You could always add the .exe file as a non-steam game) 
I can’t find the actual quote of @PatrickKlug , but he stated the buyers will get a steam key when the game is accepted by steam.
http://forum.greenheartgames.com/t/getting-windows-8-version-if-i-have-purchased-the-other/2018/5
We can base the answer on that
yeeeeeeees!
Thank you, got my answer.