I vote for an idiotic and pointless league system. Why, man, why? Because getting knocked out immediately would be bloody annoying (even though you have to lose two matches to lose a game), since it's possible just to have incredibly bad luck for no obvious reason in Worms. Plus, since not many people will be participating anyway, it allows people to play more games. Provided the whole of the world doesn't somehow acquire the game, it should even be possible for everyone to play against everyone else.
Also, I think 1-vs-1 is fine without any added modes. A "team" style game would also be good (like, two people versus two others), but perhaps that's better left until later. Like with Quake, man!
(Always with the MIQC comparisons.)