Tekken 6's producer told PlayStation Europe his team is eyeing additional DLC for the game, and it doesn't sound like he's talking about the Cardboard Tube Samurai outfit or online modes. Whatever comes out, if anything, will be free.
Asked about plans for more downloadable content, Katsuhiro Harada, the Namco Bandai producer over Tekken 6, said, "There is a strong possibility we will. However, even if we were to do so, it would be free to the end user."
The "strong possibility" qualifier would make it seem that Harada is not talking about an online cooperative scenario mode, nor network patches, both of which are in the works. Either way, if they do roll more content it's nice to know it will be free.
Tekken 6 Developer Interview [PlayStation UK via Siliconera]