Valve's marketing VP Doug Lombardi has revealed that the studio is currently in the process of working out cross-gameplay between Left 4 Dead and Left 4 Dead 2, allowing the two games to lock together like a gestalt and form Devastator.
"That's something that we're trying to work out the details of right now," he explains. "So nothing specific to say today, but we understand that it's a very valid thing to be working on and looking at."
In terms of Mods, Valve has confirmed that they will be able to migrate between the games: "With the MOD stuff, if you're making stuff for Left 4 Dead it will work in Left 4 Dead 2 with very minor amounts of work to bring it over. So we feel we've made good steps on that side and now we're looking at how we manage that for folks who buy the first game and sequel."
Going back to cross-play, this is a feature that many fans have named as a highly desirable addition to the sequel, so hopefully Valve is able to confirm its possibility soon. It may go some small way toward warming the cynics over to the new game, if Left 4 Dead 1 won't be rendered totally obsolete by the sequel's existence.