We don't have a release date set on GOG (or anywhere else for that matter),
I was initially reluctant to register to Steam just for that, but in the end I did it. That's how attractive the game is

I have a small tip though : when you go to your game's web page (not the steam pace, I mean your own page with your own domain name), there's no hint that the game has been released, and no link to Steam. It even says "the game IS BEING developed...", "it WILL feature...".
There should be a huge button in the middle that says "THE GAME HAS BEEN RELEASED, CLICK HERE TO BUY IT FROM STEAM" or something.