It was said on the kickstarter feed that supplements would be available for general release, but with no schedule attached. I was in the same boat, could only spring for the box set + some dice in the end, and I remember reading that the other books etc. would be sorted for kickstarters first, then go on general release some time after that.
At a guess they'll do the print runs both at the same time, then get the backers sorted, then stagger the commercial releases (one a month maybe) to maintain the profile of the game.