One thing I really like about your suggestion is that it separates the update-state-over-time action from the draw-UI-from-state action. I’m planning this as an ARG with some offline behavior, and I think that will pretty much require that I be able to “scrub” through time independent from the render schedule.
Per @Telinc1’s advice, I think I should avoid using Geoms, though. It’s what I’m using right now, but I will eventually care about performance.