Cave Biomes in Custom Dimensions.

You can create overworld cave biomes, but you cant for custom dimensions? I don't usually ask for help on my projects or request anything but this just feels like it would make such a big impact.

There is no plugin for this or tutorial that I know of. Of course. I am sure there's many more important things their working on than this (seriously why are yall focusing on particles-) but I would greatly appreciate and it would greatly benefit the community.