http://kotaku.com/382879/new-earthworm-jim-games-and-cartoons-thanks
So yeah. Not only is there a new Earthworm Jim game in the works, but also a new cartoon series and a movie. The old Earthworm Jim cartoon was awesome.
No specific platform(s) for the game have been announced yet.
As a side note, the first two Earthworm Jim games are slated for release on the Wii Virtual Console.