Well, this topic isn't active at all (neither is this forum for that matter ), but with the announcement of the features coming in 1.17 it seems like a good time to say something.
So um...
PRETTY CAVES! BUNDLES! CRYSTALS! CAVE FISHIES!
Pretty as these caves are, though, I don't think I'll want to mine in them. At least not the flooded and enormous ones. (or the ones covered in plants, or the ones with that creepy dark stuff... ) I'd have to leave it half-mined and that would really bug me.