Cave cracks and aquafirs should have an up-ed spawnrate in jungles.

Jungles should have up-ed cave cracks, holes, and aquafir spawnrates. The local water levels should be much higher in jungles as well.

Mountains should have caves spawn within them much more commonly and some caves should be exposed to the outside.

In cold biomes aquafirs should be entirely made of ice or at least iced on the top.
I believe this wouldn't be possible since caves will be their own biomes, though, so I believe caves should vary in temperatures (only normal caves not lush or drip caves). So some caves that have cold temperatures should have ice instead of water if they are aquafirs and hot ones should have an up-ed lava spawnrate.

A bouncy plant should also be added in caves that could bounce you up a maximum of 6 blocks when you jump on them. I'd imagine this plant would only spawn in lush caves.

Void fog and particles when you get below y0 should be added (again) just for atmosphere.