Perhaps the source code should be audited, if only to figure out what happened to the $600,000,000, but it's not clear that that requires open sourcing the code.
Now, the taxpayers purchased the codebase and the codebase could help states that did not offer a state marketplace create one. So I am very supportive of the idea of making it available to various states. But until the thing is running relatively smoothly, I don't see open sourcing it as doing anything but delaying the rollout and making it less reliable and less secure.
Update: it turns out John Oliver has taken a look at the code: http://www.youtube.com/watch?feature=player_detailpage&v=2Qt...