It is not a fully estimated thing yet if I am correct.
I believe the game will be released to people who have backed the game via Kickstarter or via their current home page. ( Pre-order)
Now in terms of Steam page release that is still unknown until they know how well it goes with the backer release and Pre-Alpha stage.
The backer release, the keys will be given to anyone who has purchased the game prior to the backer release.
So in terms, if you have pre-ordered the game before the game has been given to the backers, or if you have backed the game since the kickstarter page you will receive a key in the next few weeks or so if all goes to plan.