Writing org for this feels a bit more natural than rst, because azmodie argues for simple promoting and demoting of slides etc., and if I were to use impress.js anyway, it would be nice to make actual use of its benefits instead of just building the usual slides.

That's using TikZ mindmap and looks not very presentation-like, but the layout logic there looks like what I might want.

And by “That's using TikZ” I mean there isn't any org in there at all.