Maybe it has been suggested before, but what about a tournament-mode? Make users able to organize tournaments with private invitations. For example, users start with 0 points and a time limit, let's say 2 hours. Provide the ability to add a set of Katas which the users will have to solve during these 2 hours. The one who solves the most Katas during the period, wins! Would be great for group-seminars, workshops, etc.

(If there already exists possibilities for this, please inform me! :-))