If it's possible to transfer mods from a computer to a 360 (which, I know it is) and someone were to make another online co-op mod (like, or hopefully better than the last), wouldn't that make a type of two player mode accessable on Live?
What I'm saying is, if people used the Xbox 360's advanced hard drive software and possible a mod chip, they could get a co-op mode on their 360 over Xbox Live.
There, I just saved you hours of incoherant babbling about how I should know by now that mods will be made for the 360.