I had a sort of similar idea to what Tacronicus posted as "Opposing Outcomes," only I was thinking of it at a different angle -- as a 'meta-challenge.' In a few games I've played, the narrator has posted a series of challenges which must be completed to alter the outcome of a larger idea, each of which piece had a part to play. What if we could post the whole idea as a challenge (IE: Get off Planet X) with subchallenges within it to which the characters actually play (IE: Bribe an Official, Acquire a Ship, Meet at These Coordinates). Each of these challenges are as normal ones, able to be given however many boxes the narrator feels appropriate and have a strong/weak/neutral outcome. However, the metachallenge itself has only the number of boxes as its number of contained challenges, and the s/w/n outcome of those are what play directly into the metachallenge's completion -- by completing the normal challenges, the metachallenge boxes are also filled in and influenced toward its own s/w/n outcome.

I'd thought that it would be good to use for PvP challenges also, but Tacronicus raised a point in Opposing Challenges about having players unable to play against more than one challenge in his idea. That's a very valid point, but it wouldn't work so well for a metachallenge, since it isn't necessarily directed at PvP.

As for how would would look ... similar to what's already there, perhaps, just with the metachallenge card's outline enclosing the others. Maybe tint it a little to make it more distinct, if necessary. The challenges and metachallenge would all click to expand for details, same as they do now.

Another variation is a metachallenge that requires its steps to be done in a certain order (ie, you can't play on the Acquire the Ship challenge until you've done Bribe the Official), but this almost seems like it would be another type of metachallenge entirely (it may not have an outcome of its own, if all you're doing is requiring play order). If I had to pick one or the other, I'd stick with the first one. I know that some narrators do (both of) these now, by hand. This might just make it a little cleaner.