I'm looking for a mod that can replace the ubiquitous below-ground stone with many undulating strata of different rock types. Mods like Rockhounding add dozens of different stone variants but only distribute them in clusters and patches. In reality, the subterranean world is made up layers upon layers.
You can picture the result by removing all stone below ground and turning the world over. Then start dropping soft pancakes of different stone types into the dirt-lined hollow. Differing sizes and random placements make the layers fold and flop over each other, filling in all available space. Once everything is full, level it off, apply the bedrock, and turn the whole thing back over. Ta-da! (This should not be the actual algorithm used...)
I have an immediate need for such a mod, but further development could force all ores to generate in long veins that run along these strata or the boundaries between them.