@runevision Fantastic writeup, thanks!
Generating a good input heightmap is explicitly beyond the scope of this article, but that feels like the next logical thing to look at. I've been wondering if there's a good way to make sure that following down a slope will end up at a lake or ocean, i.e. controlling the local minima. Maybe a large scale voronoi system could determine the maxima and minima in such a way that finer scale voronois could preserve these while forking the channels between them.