I know the news caves are still in very early development, but I thought I'd share just a few things I notice when messing around in the newest snapshot. Namely, old cave generation doesn't happen below y=0, and the "cheese" cave generation doesn't happen above y=0. Both either start or stop directly at that point. The only cave generation to not have this limitation seems to be the "spaghetti" generation. I wasn't sure if this was a bug or intentional, but  I decided to put this here just in case. 

Also on a side note, the dripstone cave biome seems to not be fully integrated with the new y levels, as below y=0 no large dripstone block stalactites generate, even though plenty of stalagmites do.