Valve have just announced that the second downloadable content package arriving for Portal 2 is an 'in-game editor'. Valve released a PR statement declaring that the second DLC package is currently "in development and targeted for release early next year."
As we all know, Valve love community-created content and this new DLC is set to have some form of community functionality attached to player creations allowing players to "view, play and vote" on various levels. The editor will also allow players to create and share both single-player and co-op levels. At the moment, it is unknown how the editing will work, and whether it'll make a splash on all platforms, PC/Mac and consoles.
With Steam support on all platforms apart from the Xbox 360, the Portal 2 DLC should be released everywhere. But, we'll have to wait a little while for some clarification. Exciting news and hopefully a sign of things to come for Valve titles.