Valve seeking community input for next Left 4 Dead 2 DLC

More Left 4 Dead 2 DLC is on its way, this time with considerable input from Valve's community. Yesterday, the studio admitted over its blog that it was late in updating its zombie-survival franchise, but that it was now ready to move forward with a fairly meaty DLC release, the contents of which will be refined by fans.

The unnamed DLC pack will contain 3 campaigns from Left 4 Dead that have yet to be ported to the sequel. It will also include a new community campaign entitled Cold Stream created by Matthew Lourdelet, whose previous L4D2 creation, 2 Evil Eyes, was well received by both Valve and players.
Explaining how it plans to bring Lourdelet's creation to the masses, Valve wrote:
“He recently shared it with us and we love it so far but it isn’t done. We were tempted to have him quietly finish it with our help and release it as part of an upcoming DLC. Tempted… but we decided against that. Instead, we think we have a better idea. We want you the community to be part of the process of taking his unfinished campaign and releasing it as DLC on the Xbox 360, PC and Mac.”
True to its word, Valve has set up a dedicated Cold Stream thread, and has promised to make the unfinished add-on available for playtesting in the next few weeks.
As for an ETA, Valve added that the L4D2 DLC will be ready when it's damn well ready (aka Valve time), but that it won't be available until after Portal 2.