I know this topic has been brought up before, But I've received some interesting information via E-mail in regards to this particular topic.
Microsoft's XNA is a program designed to help create custom models/content for the Xbox 360. The Softimage program, is of course a program designed to allow you to create models for Half-Life 2.
I believe that there is some kind of connection between these two items, I don't see why Softimage would be promoting Microsoft's product unless there was a direct relationship.
In my humble opinion, there will be, once the orange box comes out, a way to play Half-Life 2 mods, on your xbox 360. Of course, they may have to be specifically created for the xbox 360, but it's a huge step forward.