Valve are known for giving away DLC on PC. Microsoft are known for charging money for avatar t-shirts. Doesn't seem like there's a good way to bring the two together, but Valve may have an idea.
"One of the things I'm thinking about is how we work within that [Xbox Live]system," Valve's Yasser Mailaka told OXM, "and one of the things I'd like to do is to allow these modules that are being released on PC to somehow integrate with Microsoft's system."
"We'll have to filter them, we can't allow any copyrighted materials, so it's going to have to go through a process", he continued. "But we're hoping perhaps we can shepherd the really popular campaigns onto 360. And you know, if they are a paid system, perhaps that could go back to the authors. I think that would be a great story".
It would be a great story! One that, knowing the 360's marketplace and Valve's propensity for daydreaming will probably never happen, but hey, you can never say never.