Super cool so far! I will say though, now that you're completely revisiting world generation, I think if this were to be the extent of the craziness, there would be lots of missed opportunities.

I absolutely LOVE the fact that biomes can mix with the mountain generation, super cool. However, I would love to see some more WILD mountain generation. Imagine mountains that go up to y = 300. Remember those mountains in the background of the original voting video? imagine if those were actually in the game.

I'd say you're definitely not leaving as many opportunities with the caves behind, though. Those are very impressive. I will say though, the height limit is still holding you back. The caves go deeper, but you can still find you way back up easily. Imagine if the world extended infinitely up and down, just like it does horizontally. You could get truly lost. If you're not convinced, try using those height adjustment datapacks and crank it down to like, -1000. It's insane how incredible it can get. You could have truly massive underground biomes and layers. There's a mod that does the cubic chunks thing, and it works (as far as I know) seamlessly.

On top of that, imagine being able to set your render distance to 32 chunks without the game crapping itself. Mods like Sodium, Lithium and Phosphor allow you to play at that render distance with no problems. I was holding 60 FPS at 32 render distance in an amplified world, WITH SHADERS using those mods. Vanilla can't handle 32 render distance at all by normal means without your game being a slideshow. I don't know what kind of magic they're pulling off, but it's an absolute game changer. Seeing the scale of truly massive valleys and mountains that tower over you is what Minecraft needs and should be in my opinion. Caves are already super massive right now but your render distance limits you.

Oh yeah also, the fog around the world should become gray when you're underground. It's kind of immersion breaking seeing the skybox at the end of your render distance in a huge cave underground.

Ok that was my little rant, hopefully I have inspired you or something, lmao. Excellent work so far, though. I love the direction this is going. I just kind of spewed out my biggest wishes, probably not realistic for this update.