Here's a final set of screenshots for now. Now that I optimized the generator to the bone for the best performance I can imagine achieving, I added a simple two-point control that lets surfaces form at the top while gradually reducing caves below height zero; In the future it would be nice to have this as a curve of points for full control over the density at particular heights, so far though it produces pretty good landscapes as is.
The next step would be texturing. I plan to approach it with a mixture between triplanar mapped materials and vertex colors for biomes, it's going to be a huge headache in either case. I wonder if shaders can be used to generate procedural textures like you can in Blender... that's gonna be quite the thing to toy with if so.