I just waded through that entire thread (slow day at work), and the tail end of it should be required reading for anyone involved in a role-playing game. It outlines where the explicitness of the MC's Agenda and Principles come from, and why they are applied the way they are applied. Fascinating stuff, and core to that all important middle ground of "where theory meets practice."
In the context of your particular game, the concept of the "Bang" might feel less forced if it stems from the result of a seasonal move rather than from some situation you have pre-fabricated. That is to say, a "Bang" is a fine and fantastic way to start a session - but it's even better if that Bang can be tied into one (or more) of the players' opening moves.
Make no mistake, though - the latter approach is harder to do, simply because it deprives you of the ability to do any prior prep-work. You may have no idea going in which seasonal moves the players will attempt, nor what the results of those moves will be a priori, so in some sense you're "winging it." But ultimately I feel like it is a more appealing approach because it places the players' choices (and the consequences thereof) in a more central position in "the plot."
I fully acknowledge that this is my own bias talking, however.
Regardless, let us know how it turns out!