Submitted my prototype for the jam in case people are interested. Here's what I'm thinking to keep the game roughly following the original SRD, but to try and make sure all the prompts have a chance to show:
1. Reroll 3d6 for each Act (I'm calling them scenes) - this keeps the probability curve the same for prompts within each act, making them all at least in theory reachable, but moving away from the cool concept of "everything from a single roll".
2. Swinging the initial roll further toward extremes by adding/subtracting more from the thread of destiny each play through. Given #1, this mostly just impacts the closing prompt (I decided to use them as openers - "episode arcs") and the acts.