Among the coming changes is the addition of computer-controlled bots to the Infected side of Versus mode, with Valve explaining that this is meant "to help out the Infected when they are down a man or two" and "will also make 1v1 Versus a bit more fun." nope
In addition, the company has been "experimenting with a solution for auto-spawning in Versus finales," such as removing auto-spawning altogether. It also cautions that such changes must be measured to see how their affect ib gameplay balance, which currently gives individual survivors a 34.56% chance of finishing the finale--a figure that drops down to 29.61% if you exclude Dark Carnival and its soon-to-be-fixed "cheese spot."
As for the most popular mode, Versus or Campaign, Valve says "it really depends on the day, as they are almost always statistically tied," and adds that work on L4D2's first downloadable add-on, "The Passing," is in "full swing" with voice recording soon.