This interview on The Morton Report kicks off a conversation that concludes with this Part 2, talking with Greg Kasavin of on Supergiant Games about Bastion. Though they did add Portal turrets to the Steam version of their action/RPG, he says that while they "intend to continue supporting the game," they don't plan on any DLC, as they "held nothing back" from the game (thanks Kotaku). Here's the quote:

No, we have no plans to extend the game in that way. As I was saying before, we held nothing back. It's meant to be a complete story, so there are no obvious extensions. We of course intend to continue supporting the game and I guess you could call something like the Portal turrets DLC. We'll continue looking at things like that which we could do, but that's it.