I've been thinking about this, and what I'm planning on doing is:
* If you order before the preorder deadline, you are guaranteed a set. These preorders will determine the production volume, and we'll make extras to handle damage/lost-in-mail/etc issues.
* If you order after the deadline, you'll go on a waitlist. You won't be guaranteed a set, your name won't appear on the discs, and you won't get it until after all the preorders have been shipped and received.
* If after that there are still any sets left (after setting aside some for handling "dog ate my set" issues) then we will sell them off on the website, but at a higher price than the preorder.
After everything is sold off I'll recalculate the budget and figure out what to do with any excess -- maybe send everyone an extra bonus gift, or use it as a rainy-day fund for future kickstarters.