The Left 4 Dead Blog announces Left 4 Dead 2 will soon incorporate Steam Workshop support, and that this will be accompanied by an expanded scripting tool:

The Steam Workshop website will allow you to browse, rate, and discuss thousands of community created add-ons and even install them directly to your game with just one click of the mouse. We are also going to try an experiment with the L4D2 Workshop that will allow content to appear in the L4D2 world even more seamlessly based on the community’s response.

To compliment the new access to maps, weapons, and items, we are also creating an expanded scripting tool to allow deeper and more varied experiences inside of Left 4 Dead 2. Similar to the current Mutations, these experiences can be laid on top of existing maps or included with brand new maps. These new style Mutations will also be available from the Steam Workshop.

All of this will also be available not just on the PC and Mac, but also for Linux users as well starting in the middle of next month and rolling out from there. We will have more details as we get closer to launch.