Hello
A couple of months ago I started to rewrite this mod such that it would allow other mods to define these surfaces. Along with that I started to work on a mod that adds a caves surface. The idea is that the player would be able to explore caves in pitch black, find dungeons and maybe even fight bosses.
It's quite an ambitious idea, and it's not done yet. I also don't have the time to work on the mod at the moment, so it'll be some time before it's done.
At this point you may understand why I'm not planning to add such features to this mod. I'm currently just maintaining this mod. Just know that once my new mod is done, implementing your ideas will be very easy, it will even be the default option.