It is an interesting idea, but from the perspective of someone who has to sell events to sponsors every month I'm not sure a slalom only tournament is very exciting to potential viewers. I'm not trying to rain on your parade, but i think we need to be careful about creating an event, that I've heard described by several people I've introduced to the sport, as "fun to do but as entertaining as watching paint dry."
I think that nationals should be 3 weekend events. One for each event, and that way you could play with the format a lot more. If you did that based upon last years divisions, in most cases trick and jump could almost be bracketed like the NCAA basketball tournament. And you could probably have a head to head finals for the slalom one.