Seeing as caves haven't received an update since 1.13 (underwater caves) and cave gen hasn't received a fundamental change since 1.7 (RIP Swiss cheese), it can be safely speculated that caves will be updated soon. However, I was a little impatient and wanted to do it sooner. So, this mod exists.
Cave Update aims to bring as much content - probably even more - to caves as 1.16 brought to the Nether. I know that's a big scope, but I think it's possible.
At the moment, things are early, but things such as a config file will be added in the future.
Check the pictures tab for current features!
FAQ (Read this before asking anything!)
Q: Can you make this for Forge?
A: Short answer: no. Long answer: Remaking an already massive mod for another mod loader is a massive undertaking and something I won't have much time for, but you are more than welcome to port it yourself using the source assets and code.
Q: What's next?
A: Well, whatever I feel fits best into the mod. Current ideas include: biome-exclusive ores, craftable totems, a poison lake biome, more cave reed wood items, underground mushrooms, giant bats, other giant creatures, tougher mobs, etc.
Q: Can I use this with other cave mods?
A: This mod significantly alters cave generation and probably won't play well with other cave mods. Sorry.
Q: Can I marry you?