Speaking with Team17 designer Gavin Hood at the Rezzed conference, Strategy Informer learned that rather than create post-release DLC for Worms: Clan Wars, they are concentrating on mod tool and Steam Workshop support to allow the community to create any such content for themselves. Here's the excerpt they've posted from a larger interview they will publish soon:

Gavin Hood: We’ve got no plans for DLC for the game at all, we’re not hiding anything away. Instead we’ve got full Steam Workshop support out of the box planned for the game so people can make their own items, make their own speech banks, make Clan outfits and share all these. Post launch but within the launch window we’re going to release a Mission Toolkit, so we give all players access to the contraptions and the machinery…

Strategy Informer: So they can make single-player stuff too?

Gavin Hood: Yes, single-player missions as well. It seemed kind of the obvious thing to do!