For almost two years I've been thinking about a conversation I had with Robin Laws about how RPGs and story structures relate. He's made lots of comments about it both before and after, so the message continues to come back to me. The nub of the point is that if an RPG is to be a story-telling exercise, it needs to contain rules that go with the ebb and flow of good story telling. There are plenty of games that seem to contain rules like this. Just as one example, Spirit of the Century includes the potential for character aspects to be compelled, thus simulating the notion that the protagonist will endure hardship in the leadup to triumph. Compel enough aspects to get the hero in trouble and this gives the hero enough fate points to overcome even the most significant obstacle.
In order to incorporate this into Siege, I'm looking into an opportunity that is not character driven (like Spirit) and not story driven (as though the plot has a form to follow). It's... well, you'll have to wait until I flesh it out some more.