What I envision is something like Matt's Ft. Pitt Hi-Railers setup, although modified for On30. Those modules appear to have a purpose over and above their switching activity potential, and that's what I'm looking for.
I would be using small motive power, even though I have examples of most everything Bachmann has produced in On30. I'm thinking primarily of gas mechanicals, 0-4-0s, 0-4-2s, and the like.