I think it would be a smart move for Amazon to purchase them because it would give them an easy way to integrate their fulfillment center into the equation. For smaller products it would be too expensive unless they provided a special project rate; $1 picking fees add up quickly when you have multiple add-ons.
Kickstarter is too cool for that though, I honestly can't see them selling to anyone. Which they should, they lucked out and I think their business side is a bit lost. It will only take one competitor that is able to catch enough market share to bring them down. It may take a couple years, but the way they mismanage their project creators, they'll have to change before the next big thing comes along.