I'm looking into that. I don't want you to pay twice.
I'm new to how Steam does things, but I think I can request N amount of keys in bulk once the game is out. Tho I'm unfamiliar with the process.
So don't worry, in theory you can still buy the game here, and I'll see that you still receive a key when the game is out. Or, you can wait until the Steam release and buy the game there.
I'll keep you updated.