"held nothing back," it's a "complete story".
There are "no obvious extensions," though they'll "continue supporting" the RPG of course. The Steam version included Portal turrets which they "guess" is DLC.
Bastion is quite a unique action-RPG as every action the player takes is narrated. Portal turrets were included as bonus content for the Steam version of the game.
"No, we have no plans to extend the game in that way. As I was saying before, we held nothing back," said Greg Kasavin of Supergiant Games in an interview.
"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."
Bastion released on Xbox 360 and PC in July and August respectively.